feat: select instance via advanced filter

It would be useful to have something like `--filters` from `aws ec2 describe-instances` for selecting an instance to connect to. In my case, I am creating generic connection patterns for internal users, and hard-coding an instance id in documentation isn't ideal.

An issue is that a filter result isn't necessarily unique, I feel that mssh aborting with a message if the number of results for the filter is not equal to 1 would suffice to the principle of least surprise.