Merge branch '383126-remove-disable_metric_dashboard_refresh_rate-feature-flag' into 'master'

Remove `disable_metric_dashboard_refresh_rate ` feature flag & feature

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/105496



Merged-by: Felipe Artur <fcardozo@gitlab.com>
Approved-by: Sarah Yasonik <syasonik@gitlab.com>
Approved-by: Fernando Arias <farias@gitlab.com>
Approved-by: Ezekiel Kigbo <3397881-ekigbo@users.noreply.gitlab.com>
Approved-by: Felipe Artur <fcardozo@gitlab.com>
Co-authored-by: Laurent Deketelaere <laurent@geturl.net>