Merge branch 'cngo-replace-issuableTypes' into 'master'

Replace issuableTypes object with TYPE_EPIC constant

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/112322



Merged-by: Phil Hughes <me@iamphill.com>
Approved-by: Stanislav Lashmanov <slashmanov@gitlab.com>
Approved-by: Phil Hughes <me@iamphill.com>
Reviewed-by: Coung Ngo <cngo@gitlab.com>
Co-authored-by: Coung Ngo <cngo@gitlab.com>