Add api to lookup epics by reaction emoji

Merged Alex Ives requested to merge alexives/7783/filter_epics_by_reaction_emoji_in_api into master

What does this MR do?

This adds my_reaction_emoji as an option when using the epics finder and adds an option to to the epics endpoint as a small part of #7783

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Just adding an api, nothing that exercises it.

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
Edited by Peter Leitzen