Introduce Feature Flags for replacement of ACE with Monaco

In the first batch of "Use Monaco for all file/code editing to create unified editing experience" works, we are dealing with 3 particular places to replace ACE with Monaco:

• Snippets: :monaco_snippets
• Blobs: :monaco_blobs
• Setting CI/CD configuration: :monaco_ci

This Issue should introduce 3 distinctive feature flags for every replacement on the list for a better controllable transition.