Login-Page: Server field should be optional

[SchoolGuy]

Is your feature request related to a problem? Please describe.

If a user only has one Cobbler instance it should be possible to have a config file on the server that is optionally present that hardcodes the URL for the access. The server field should be invisible then.

Describe the solution you'd like

See above. Additionally it should be possible to set a list of servers and have a dropdown to choose from.

Describe alternatives you've considered

None

Additional context

None