Merge branch 'updated-secure-files-docs-with-experimental-status' into 'master'

Update Project-level Secure Files docs to note it is an experimental feature

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/98540



Merged-by: Marcel Amirault <mamirault@gitlab.com>
Approved-by: Marcel Amirault <mamirault@gitlab.com>
Co-authored-by: Darby Frey <darbyfrey@gmail.com>