Merge branch 'psi-fields' into 'master'

List of custom fields on work items settings page

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/169578



Merged-by: Natalia Tepluhina <ntepluhina@gitlab.com>
Approved-by: Jack Chapman <jachapman@gitlab.com>
Approved-by: Buck O'Leary <bucoleary@gitlab.com>
Approved-by: Natalia Tepluhina <ntepluhina@gitlab.com>
Approved-by: Nick Leonard <nleonard@gitlab.com>
Reviewed-by: Simon Knox <simon@gitlab.com>
Reviewed-by: Heinrich Lee Yu <heinrich@gitlab.com>
Reviewed-by: Natalia Tepluhina <ntepluhina@gitlab.com>
Reviewed-by: Nick Leonard <nleonard@gitlab.com>
Co-authored-by: Simon Knox <simon@gitlab.com>