feat: update sql server flex configuration for user and database (#46)

## Description

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At least please give us some description what you are trying to achieve and why your change is needed. -->

relates to #1234

## Checklist

- [ ] Issue was linked above
- [ ] Code format was applied: `make fmt`
- [ ] Examples were added / adjusted (see `examples/` directory)
- [x] Docs are up-to-date: `make generate-docs` (will be checked by CI)
- [ ] Unit tests got implemented or updated
- [ ] Acceptance tests got implemented or updated (see e.g. [here](f5f99d1709/stackit/internal/services/dns/dns_acc_test.go))
- [x] Unit tests are passing: `make test` (will be checked by CI)
- [x] No linter issues: `make lint` (will be checked by CI)

Reviewed-on: #46
Reviewed-by: Marcel_Henselin <marcel.henselin@stackit.cloud>
Co-authored-by: Andre Harms <andre.harms@stackit.cloud>
Co-committed-by: Andre Harms <andre.harms@stackit.cloud>

stackit/internal/services/sqlserverflexbeta/utils/util.go

@@ -0,0 +1,47 @@
+package utils
+
+import (
+	"context"
+	"fmt"
+
+	sqlserverflex "tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/pkg_gen/sqlserverflexbeta"
+
+	"github.com/hashicorp/terraform-plugin-framework/diag"
+	"github.com/stackitcloud/stackit-sdk-go/core/config"
+	"tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/stackit/internal/core"
+	"tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/stackit/internal/utils"
+)
+
+func ConfigureClient(
+	ctx context.Context,
+	providerData *core.ProviderData,
+	diags *diag.Diagnostics,
+) *sqlserverflex.APIClient {
+	apiClientConfigOptions := []config.ConfigurationOption{
+		config.WithCustomAuth(providerData.RoundTripper),
+		utils.UserAgentConfigOption(providerData.Version),
+	}
+	if providerData.SQLServerFlexCustomEndpoint != "" {
+		apiClientConfigOptions = append(
+			apiClientConfigOptions,
+			config.WithEndpoint(providerData.SQLServerFlexCustomEndpoint),
+		)
+	} else {
+		apiClientConfigOptions = append(apiClientConfigOptions, config.WithRegion(providerData.GetRegion()))
+	}
+	apiClient, err := sqlserverflex.NewAPIClient(apiClientConfigOptions...)
+	if err != nil {
+		core.LogAndAddError(
+			ctx,
+			diags,
+			"Error configuring API client",
+			fmt.Sprintf(
+				"Configuring client: %v. This is an error related to the provider configuration, not to the resource configuration",
+				err,
+			),
+		)
+		return nil
+	}
+
+	return apiClient
+}

stackit/internal/services/sqlserverflexbeta/utils/util_test.go

@@ -0,0 +1,97 @@
+package utils
+
+import (
+	"context"
+	"os"
+	"reflect"
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-framework/diag"
+	sdkClients "github.com/stackitcloud/stackit-sdk-go/core/clients"
+	"github.com/stackitcloud/stackit-sdk-go/core/config"
+	sqlserverflex "tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/pkg_gen/sqlserverflexbeta"
+
+	"tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/stackit/internal/core"
+	"tf-provider.git.onstackit.cloud/stackit-dev-tools/terraform-provider-stackitprivatepreview/stackit/internal/utils"
+)
+
+const (
+	testVersion        = "1.2.3"
+	testCustomEndpoint = "https://sqlserverflex-custom-endpoint.api.stackit.cloud"
+)
+
+func TestConfigureClient(t *testing.T) {
+	/* mock authentication by setting service account token env variable */
+	os.Clearenv()
+	err := os.Setenv(sdkClients.ServiceAccountToken, "mock-val")
+	if err != nil {
+		t.Errorf("error setting env variable: %v", err)
+	}
+
+	type args struct {
+		providerData *core.ProviderData
+	}
+	tests := []struct {
+		name     string
+		args     args
+		wantErr  bool
+		expected *sqlserverflex.APIClient
+	}{
+		{
+			name: "default endpoint",
+			args: args{
+				providerData: &core.ProviderData{
+					Version: testVersion,
+				},
+			},
+			expected: func() *sqlserverflex.APIClient {
+				apiClient, err := sqlserverflex.NewAPIClient(
+					config.WithRegion("eu01"),
+					utils.UserAgentConfigOption(testVersion),
+				)
+				if err != nil {
+					t.Errorf("error configuring client: %v", err)
+				}
+				return apiClient
+			}(),
+			wantErr: false,
+		},
+		{
+			name: "custom endpoint",
+			args: args{
+				providerData: &core.ProviderData{
+					Version:                     testVersion,
+					SQLServerFlexCustomEndpoint: testCustomEndpoint,
+				},
+			},
+			expected: func() *sqlserverflex.APIClient {
+				apiClient, err := sqlserverflex.NewAPIClient(
+					utils.UserAgentConfigOption(testVersion),
+					config.WithEndpoint(testCustomEndpoint),
+				)
+				if err != nil {
+					t.Errorf("error configuring client: %v", err)
+				}
+				return apiClient
+			}(),
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(
+			tt.name, func(t *testing.T) {
+				ctx := context.Background()
+				diags := diag.Diagnostics{}
+
+				actual := ConfigureClient(ctx, tt.args.providerData, &diags)
+				if diags.HasError() != tt.wantErr {
+					t.Errorf("ConfigureClient() error = %v, want %v", diags.HasError(), tt.wantErr)
+				}
+
+				if !reflect.DeepEqual(actual, tt.expected) {
+					t.Errorf("ConfigureClient() = %v, want %v", actual, tt.expected)
+				}
+			},
+		)
+	}
+}