Add documentation for the Go API design

docs/design-go-api.md

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+# Go API Design documentation
+
+## Overview
+
+This document presents the high-level user API for the Go-Wrapper client library. Specifically, it demonstrates how the user connects to Redis, executes requests, receives responses, and checks for errors.
+
+## Requirements
+
+- The minimum supported Go version will be 1.18. This version was chosen because it added support for generics, including type constraints and type sets.
+- The API will be thread-safe.
+- The API will accept as inputs all [RESP3 types](https://github.com/redis/redis-specifications/blob/master/protocol/RESP3.md).
+- The API will attempt authentication, topology refreshes, reconnections, etc., automatically. In case of failures concrete errors will be returned to the user.
+
+# Use Cases
+
+### Case 1: Create Redis client and connect
+
+```go
+var config *StandaloneClientConfiguration = glide.NewClientConfiguration()
+    WithAddress(glide.AddressInfo{Host: host, Port: port}).
+    WithUseTLS(true)
+
+// Create a client and connect
+var client *glide.RedisClient
+var err error
+client, err = glide.CreateClient(config)
+```
+
+### Case 2: Connection to Redis fails with ClosingError
+```go
+var client *glide.RedisClient
+var err error
+client, err := glide.CreateClient(config)
+
+// User can check specifically for a ClosingError:
+if err != nil {
+    closingErr, isClosingErr := err.(glide.ClosingError)
+    if isClosingErr {  
+        log.Fatal("Failed to connect to Redis: " + closingErr.Error())
+    }
+}
+
+// Or user can simply log the error message:
+if err != nil {
+    log.Fatal("Redis client failed with: " + err.Error())
+}
+```
+
+### Case 3: Connect to Redis with deferred cleanup
+```go
+var client *glide.RedisClient
+var err error
+client, err = glide.CreateClient(config)
+if err != nil {
+    log.Fatal("Redis client failed with: " + err.Error())
+}
+
+defer client.Close()
+
+// continue using client...
+```
+
+### Case 4: Connect to Redis cluster
+```go
+var config *glide.ClusterClientConfiguration
+config = glide.NewClusterClientConfiguration().
+    WithAddress(glide.AddressInfo{Host: host1, Port: port1}).
+    WithAddress(glide.AddressInfo{Host: host2, Port: port2}).
+    WithUseTLS(true)
+
+var client *glide.RedisClusterClient
+var err error
+client, err = glide.CreateClusterClient(config)
+```
+
+### Case 5: Get(key) from connected RedisClient
+```go
+result, err := client.Get("apples")
+```
+
+### Case 6: Set(key, value) from connected RedisClient
+```go
+// Without setOptions
+err := client.Set("apples", "oranges")
+
+// With setOptions
+var setOptions *glide.SetOptions
+setOptions = glide.NewSetOptions().
+    WithReturnOldValue(true)
+oldValue, err := client.SetWithOptions("apples", "oranges", setOptions)
+```
+
+### Case 7: Get(key) from a disconnected RedisClient
+Return a glide.ConnectionError if the RedisClient is closed/disconnected
+```go
+result, err := client.Get("apples")
+if err != nil {
+    connErr, isConnErr := err.(glide.ConnectionError)
+    if isConnErr {  
+        log.Fatal("RedisClient get failed with: " + connErr.Error())
+    }
+}
+```
+
+### Case 8: Send custom command to RedisClient
+```go
+var result interface{}
+var err error
+
+result, err = client.CustomCommand([]{"GET", "apples"})
+if err != nil {
+    log.Fatal("RedisClient failed to execute custom command with: " + err.Error())
+}
+
+strResult, isString := result.(string)
+if !isString {
+    log.Fatal("Expected result to be of type string but the actual type was: " + reflect.TypeOf(result))
+}
+```
+
+### Case 9: Send transaction to RedisClient
+```go
+transaction := glide.NewTransaction()
+transaction.Get("apples")
+transaction.Get("pears")
+transaction.Set("cherries", "Bing")
+
+var result []interface{}
+var err error
+result, err = client.Exec(transaction)
+if err != nil {
+    log.Fatal("Redis client transaction failed with: " + err.Error())
+}
+
+firstResponse := result[0]
+secondResponse := result[1]
+thirdResponse := result[2]  // evaluates to nil
+```
+
+### Case 10: Send Get request to a RedisClusterClient with one address
+```go
+var config *glide.ClusterClientConfiguration
+config = glide.NewClusterClientConfiguration().
+    WithAddress(glide.AddressInfo{Host: host, Port: port}).
+    WithUseTLS(true)
+
+// Create a client and connect
+var client *glide.RedisClusterClient
+var err error
+client, err = glide.CreateClusterClient(config)
+if err != nil {
+    log.Fatal("Redis client failed with: " + err.Error())
+}
+
+result, err := client.Get("apples")
+```
+
+### Case 11: Send Ping request to a RedisClusterClient with multiple addresses
+```go
+var config *glide.ClusterClientConfiguration
+config = glide.NewClusterClientConfiguration().
+    WithAddress(glide.AddressInfo{Host: host1, Port: port1}).
+    WithAddress(glide.AddressInfo{Host: host2, Port: port2}).
+    WithUseTLS(true)
+
+// Create a client and connect
+var client *glide.RedisClusterClient
+var err error
+client, err = glide.CreateClusterClient(config)
+if err != nil {
+    log.Fatal("Redis client failed with: " + err.Error())
+}
+
+// Without message or route
+result, err := client.Ping()
+
+// With message
+result, err := client.PingWithMessage("Ping received")
+
+// With route
+result, err := client.PingWithRoute(glide.NewRoute(glide.AllNodes))
+
+// With message and route
+result, err := client.PingWithMessageAndRoute("Ping received", glide.NewRoute(glide.AllNodes))
+```
+
+### Case 12: Get(key) encounters a TimeoutError
+```go
+result, err := client.Get("apples")
+if err != nil {
+    timeoutErr, isTimeoutErr := err.(glide.TimeoutError)
+    if isTimeoutErr {  
+        // Handle error as desired
+    }
+}
+```
+
+### Case 13: Get(key) encounters a ConnectionError
+```go
+result, err := client.Get("apples")
+if err != nil {
+    connErr, isConnErr := err.(glide.ConnectionError)
+    if isConnErr {  
+        // Handle error as desired
+    }
+}
+```
+
+# API Design
+
+## Presentation
+
+![API Design](img/design-go-api.svg)