Add system datasource

This will allow terraform datasources such as:

```
data "hpegl_pc_system" "my_system" {
  name = "array-foo"
}
```

We will use the 'id' of the system datasource when
creating other resources.

internal/constants/constants.go

@@ -5,4 +5,5 @@ package constants
 const (
 	ProviderType  = "hpegl"
 	ProviderBlock = "pc"
+	NameFilter    = "name eq "
 )

internal/datasources/system/data_source.go

@@ -0,0 +1,157 @@
+// (C) Copyright 2024 Hewlett Packard Enterprise Development LP
+
+//go:build experimental
+
+package system
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/HewlettPackard/hpegl-pcbe-terraform-resources/internal/client"
+	"github.com/HewlettPackard/hpegl-pcbe-terraform-resources/internal/constants"
+	"github.com/HewlettPackard/hpegl-pcbe-terraform-resources/internal/sdk/systems/privatecloudbusiness"
+	"github.com/hashicorp/terraform-plugin-framework/datasource"
+	"github.com/hashicorp/terraform-plugin-framework/types"
+	"github.com/hashicorp/terraform-plugin-log/tflog"
+)
+
+// Ensure provider defined types fully satisfy framework interfaces.
+var _ datasource.DataSource = &DataSource{}
+
+func NewDataSource() datasource.DataSource {
+	return &DataSource{}
+}
+
+// DataSource defines the data source implementation.
+type DataSource struct {
+	client *client.PCBeClient
+}
+
+func (s *DataSource) Metadata(
+	ctx context.Context,
+	req datasource.MetadataRequest,
+	resp *datasource.MetadataResponse,
+) {
+	resp.TypeName = req.ProviderTypeName + "_system"
+}
+
+func (s *DataSource) Schema(
+	ctx context.Context,
+	req datasource.SchemaRequest,
+	resp *datasource.SchemaResponse,
+) {
+	resp.Schema = SystemDataSourceSchema(ctx)
+}
+
+func (s *DataSource) Configure(
+	ctx context.Context,
+	req datasource.ConfigureRequest,
+	resp *datasource.ConfigureResponse,
+) {
+	// Prevent panic if the provider has not been configured.
+	if req.ProviderData == nil {
+		tflog.Warn(ctx, "provider has not been configured.")
+
+		return
+	}
+
+	s.client = req.ProviderData.(*client.PCBeClient)
+}
+
+func createNameFilter(name string) string {
+	return constants.NameFilter + name
+}
+
+func getSystemByName(
+	ctx context.Context,
+	client client.PCBeClient,
+	name string,
+) (privatecloudbusiness.V1beta1SystemsGetResponse_itemsable, error) {
+	sysClient, _, err := client.NewSysClient(ctx)
+	if err != nil {
+		tflog.Error(ctx, "failed to create client")
+
+		return nil, err
+	}
+
+	filter := createNameFilter(name)
+	qp := privatecloudbusiness.V1beta1SystemsRequestBuilderGetQueryParameters{}
+	qp.Filter = &filter
+	grc := &privatecloudbusiness.V1beta1SystemsRequestBuilderGetRequestConfiguration{}
+	grc.QueryParameters = &qp
+	systems, err := sysClient.PrivateCloudBusiness().
+		V1beta1().
+		Systems().
+		GetAsSystemsGetResponse(ctx, grc)
+
+	if systems.GetTotal() == nil {
+		msg := "total is nil"
+		tflog.Error(ctx, msg)
+
+		return nil, errors.New(msg)
+	}
+
+	total := *(systems.GetTotal())
+	if total != 1 {
+		msg := fmt.Sprintf(
+			"required 1 system with name %s, got %d systems", name, total,
+		)
+		tflog.Error(ctx, msg)
+
+		return nil, errors.New(msg)
+	}
+
+	return systems.GetItems()[0], err
+}
+
+func (s *DataSource) Read(
+	ctx context.Context,
+	req datasource.ReadRequest,
+	resp *datasource.ReadResponse,
+) {
+	var data SystemModel
+
+	resp.Diagnostics.Append(req.Config.Get(ctx, &data)...)
+
+	if resp.Diagnostics.HasError() {
+		return
+	}
+
+	client := *s.client
+	system, err := getSystemByName(ctx, client, data.Name.ValueString())
+	if err != nil {
+		resp.Diagnostics.AddError(
+			"error reading system",
+			"unexpected error: "+err.Error(),
+		)
+
+		return
+	}
+
+	name := system.GetName()
+	if name == nil {
+		resp.Diagnostics.AddError(
+			"error reading system",
+			"system name is nil",
+		)
+
+		return
+	}
+
+	id := system.GetId()
+	if id == nil {
+		resp.Diagnostics.AddError(
+			"error reading system",
+			"system id is nil",
+		)
+
+		return
+	}
+
+	data.Name = types.StringValue(*name)
+	data.Id = types.StringValue(*id)
+
+	resp.Diagnostics.Append(resp.State.Set(ctx, &data)...)
+}