JOC Cockpit should deny invalid hostname in Git configuration

Current Situation

it is possible to store invalid git server names in the Git configuration. For example if users specify https://github.com instead of github.com.

Desired Behavior

JOC Cockpit should show an error message if an invalid git server name like https://github.com is used as the value in the Git configuration. 

Maintaner Note

This entry for the git server is not an URI format, therefore a protocol is not part of the entry. Only hostname and optionally a colon followed by a port are allowed.

Git Server name format: HOST(:PORT)