Add a TeamCity commit hook functionality
By default TeamCity (TC) uses fixed-time polling to check for the changes in VCS, if you have a lot of repos (>50) it could produce a significant additional load to the GitLab and TC itself.
To fix the issue TC has commit hooks which allow it to know if something has changed in VCS, which leads to the reduced amount of connections to GitLab in the end.
Currently, it's possible to configure hooks via generic hooks settings in GitLab, but it requires to have visible plain-text authentication credentials right in the hook target url since TC supports only basic auth for the API calls.
To simplify configuration for the end user and because of security reasons it would be nice for TeamCity integration plugin to be able to setup hooks.