If the request wasn't initiated by gitlab we shouldn't add the new
identity to the user, and instead show that we weren't able to link
the identity to the user.

This should fix: https://gitlab.com/gitlab-org/gitlab-ce/issues/56509

Signed-off-by: NRémy Coutable <remy@rymai.me>

Enables frozen string for the following files:

* lib/generators/**/*.rb
* lib/gitaly/**/*.rb
* lib/google_api/**/*.rb
* lib/haml_lint/**/*.rb
* lib/json_web_token/**/*.rb
* lib/mattermost/**/*.rb
* lib/microsoft_teams/**/*.rb
* lib/object_storage/**/*.rb
* lib/omni_auth/**/*.rb
* lib/peek/**/*.rb
* lib/rouge/**/*.rb
* lib/rspec_flaky/**/*.rb
* lib/system_check/**/*.rb

Partially addresses #47424.

* Replace `require` or `require_relative` with `require_dependency`
* Remove unneeded `autoload`

See
http://guides.rubyonrails.org/autoloading_and_reloading_constants.html
for more info.
Signed-off-by: NRémy Coutable <remy@rymai.me>