Update data_source.go | Use id (member ID) instead of userId as per SignalFx API documentation (#606)

* Update data_source.go | Use id (member ID) instead of userId as per SignalFx API documentation

Updated the code to use id (member ID) instead of userId in accordance with the SignalFx Observability API documentation. The id field uniquely identifies a member and should be used in all references. This ensures consistency and aligns with the latest API expectations.
Reference: 
https://dev.splunk.com/observability/reference/api/organizations/latest

* Update data_source_test.go

Updating the test file to use Id instead of UserId

Author: anuragmuley

internal/definition/organization/data_source.go

@@ -50,7 +50,7 @@ func datasourceRead(ctx context.Context, rd *schema.ResourceData, meta any) diag
 
 			for _, u := range results.Results {
 				tflog.Debug(ctx, "Retrieved user details", tfext.NewLogFields().JSON("user", u))
-				users = append(users, u.UserId)
+				users = append(users, u.Id)
 			}
 
 			if offset >= int(results.Count) {

internal/definition/organization/data_source_test.go

@@ -85,7 +85,7 @@ func TestDataSourceRead(t *testing.T) {
 					_ = json.NewEncoder(w).Encode(&organization.MemberSearchResults{
 						Count: 1,
 						Results: []*organization.Member{
-							{FullName: "user 01", UserId: "AAAAAAAA", Email: "user-01@example.com"},
+							{FullName: "user 01", Id: "AAAAAAAA", Email: "user-01@example.com"},
 						},
 					})
 				},