Merge branch 'eduardosanz/alert12' into 'master'

Replace `flash` imports to `alert` - 12/36

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/113668



Merged-by: Florie Guibert <fguibert@gitlab.com>
Approved-by: Florie Guibert <fguibert@gitlab.com>
Approved-by: Rahul Chanila <rchanila@gitlab.com>
Reviewed-by: Florie Guibert <fguibert@gitlab.com>
Co-authored-by: Eduardo Sanz García <esanz-garcia@gitlab.com>