Adds error tracking api
Adds two new resources and a data source for managing GitLab integrated error tracking:
gitlab_project_error_tracking_settings: enables/disables integrated error tracking for a project. Uses PUT on create (GitLab 15.10+) to initialize the settings record when none exists, and PATCH on update.gitlab_project_error_tracking_client_key: manages error tracking client keys (DSN credentials) for a project.data.gitlab_project_error_tracking_settings: reads current error tracking settings for referencing in other resources.
Also enables the integrated_error_tracking feature flag and
error_tracking_enabled config in the test environment setup.
Closes #457 (closed)