Check if the database exists for feature gates

What does this MR do?

Before calling out to the database to check if a feature is enabled or not, first check if the database exists.

This allows us to use feature checks during the setup of the application.

This is used in !21492 (merged) to avoid failures like this one: https://gitlab.com/reprazent/gitlab-ee/-/jobs/392670677

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers