The input validation is a bit too aggressive on handles

[Monviech]

The input validation is a bit too aggressive on the handles:

• foo.example.com.443
• foo.example.com.8443

should both be allowed to have an empty handle, but right now the input validation forbids that. Workaround is giving one of them /* as handle, that's essentially the same thing.

The input validation has to be made a little more lenient on there.

Originally posted by @Monviech in https://github.com/Monviech/os-caddy-plugin/issues/43#issuecomment-1860043443

• [x] Remove input validation on handles altogether because it doesn't matter there. Caddy will start even if handles aren't unique.

[Monviech]

https://github.com/Monviech/os-caddy-plugin/pull/51