Merge branch 'georgekoltsov/add-feature-flag-parallelized-project-export-worker' into 'master'

Add parallel_project_export feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145165



Merged-by: Rodrigo Tomonari <rtomonari@gitlab.com>
Approved-by: Sam Word <sword@gitlab.com>
Approved-by: Rodrigo Tomonari <rtomonari@gitlab.com>
Co-authored-by: George Koltsov <gkoltsov@gitlab.com>