Add a Gitlab::Json wrapper

What does this MR do?

Introduce a Gitlab::Json wrapper to wrap all usage of JSON going forward. This is related to #211671 (closed) and !29705 (merged).

By swapping to a wrapper we can handle deprecated parser usage in the app and then upgrade our JSON dependencies. The deprecated usage handler will be added in another iteration.

Screenshots

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related #211671 (closed)