Implement warnings for deprecated keywords

What does this MR do and why?

This is Phase 1 for the CI Config deprecation process.

• Add the warnings field to the CiConfigResolver which the frontend will use to display the warning.
• Add a key to the UserCallout model
• Update all the usage of types to stages in specs
• Add the ability to have a deprecation keyword and added the information to the types entry
• Add an AppLogger to track usage of the keyword for Phase 3

How to set up and validate locally

This is purely backend, so no warning will be shown.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.