Merge branch '414523-refactor-epic-header' into 'master'

Refactor EpicHeader to use IssuableHeader

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/126204



Merged-by: Jose Ivan Vargas <jvargas@gitlab.com>
Approved-by: Rajan Mistry <rmistry@gitlab.com>
Approved-by: Jose Ivan Vargas <jvargas@gitlab.com>
Approved-by: Andrejs Cunskis <acunskis@gitlab.com>
Reviewed-by: Coung Ngo <cngo@gitlab.com>
Reviewed-by: Rajan Mistry <rmistry@gitlab.com>
Co-authored-by: Coung Ngo <cngo@gitlab.com>