feat(go): Add configurable packageLayout setting

[amckinney]

This adds support for a few new configuration options, all of which are shown below:

# generators.yml
- name: fern-api/fern-go-sdk
  version: 0.36.0
  config:
    packageLayout: flat
    clientName: Acme
    clientConstructorName: New

By default, the Go SDK generates each nested client into a separate package to maximize backwards compatibility as the API evolves over time. However, some users acknowledge the risk and would prefer to have everything exported from the top-level package.

With the packageLayout: flat setting, the generated SDK will all be deposited at the root of the module, and the client can be constructed like so:

package main

import (
  "context"
  "fmt"
  "log"

  acme "github.com/acme/acme-go"
)
func main() {
  client := acme.New()
  response, err := client.GetUser(
    context.Background(),
    &acme.GetUserRequest{
      ID: "85307b0b-094b-41b5-b61d-347ca15e5da2",
    },
  )
  if err != nil {
    log.Fatal(err)
  }
  fmt.Println(response)
}

[github-actions]

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