Serverless custom roles and spaces tests

[jeramysoucy]

Summary

Implements serverless feature flag tests for custom roles and suctom spaces as part of the feature flag test configs. These tests are minimal because custom roles and custom spaces will eventually be enabled in production, and the full stateful test suites should be adapted to deployment agnostic tests if possible.

API Integration Tests

• x-pack/test_serverless/api_integration/test_suites/common/management/multiple_spaces_enabled.ts
• x-pack/test_serverless/api_integration/test_suites/common/platform_security/roles_routes_feature_flag.ts

Functional Tests

• x-pack/test_serverless/functional/test_suites/common/platform_security/roles.ts
• x-pack/test_serverless/functional/test_suites/common/spaces/multiple_spaces_enabled.ts