json gem upgrade to 2.3.0

What does this MR do?

This upgrades the json gem to 2.3.0, which changes how it handles certain forms of data. This also adds support for a legacy_mode flag when parsing, which can be used to handle expectations that use the old form of parsing. These flags have already been added to known problem areas that cause the specs to fail.

The functionality of legacy_mode can be disabled by toggling the json_wrapper_legacy_mode feature flag.

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)