Add Gitaly info-ref cache feature flags

What does this MR do?

This change adds two new feature flags to enable new features in Gitaly for the caching of the info-ref upload pack RPC.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

These feature flags should not affect quality or performance until enabled. Upon enablement, they are designed to increase the performance of the Git HTTP info-ref advertisement when used with the appropriate version of Gitaly (see gitaly!1366 (merged)).

Additional test coverage in GitLab-CE should not be necessary since the cache feature should be transparent to clients (i.e. GitLab Rails).

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

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

Part of: gitaly#1631 (closed)