Merge branch 'eduardosanz/rename-flash-to-alert' into 'master'

Rename `flash.js` to `alert.js`

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/109449



Merged-by: Vitaly Slobodin <vslobodin@gitlab.com>
Approved-by: Diana Zubova <dzubova@gitlab.com>
Approved-by: Vitaly Slobodin <vslobodin@gitlab.com>
Reviewed-by: Vitaly Slobodin <vslobodin@gitlab.com>
Reviewed-by: Eduardo Sanz García <esanz-garcia@gitlab.com>
Co-authored-by: Eduardo Sanz García <esanz-garcia@gitlab.com>