Feature request - enforce comment and author format in silence form

[Turgon37]

Hello,

In silences ACLs, we have a lots of configuration on alerts labels matcher, it's should be great to allow rules on comment and author format.
https://github.com/prymitive/karma/blob/main/docs/ACLs.md#configuration-syntax

• Author field is pre-filled by current username (if authentication is configured), can we have a way to disable input field, to prevent manual changes ?

• Can we apply a regexp on comment field, for example to ensure a ticket number is associated with a silence ?