Add the current username to GDPR failure messages in git and API calls
Sometimes the user that is currently logged in in the browser is different from the one used for accessing the API our git.
To make it clearer which user should accept the terms, we should output the current username in the error message
A suggestion by @gooutkanban in https://gitlab.com/gitlab-org/gitlab-ce/issues/46585#note_74560110
/cc @victorwu