This new project_feature will be used to allow users to configure the
visibility of metrics dashboards in their projects.

- Add metrics_dashboard_access_level to safe model attributes.

- Update spec to audit metrics_dashboard_access_level.

- Add a few supporting methods for metrics_dashboard_access_level.

- Fix audit specs.

- Remove an instantiation of Project in a migration spec that was
breaking the spec.

- Add new access_level to project_feature_spec.

- Add metrics access_level to the project_feature_spec.rb.

- Add changelog entry

- Use with_lock_retries.