kresd6 regression: subtree regex to strict, fails with underscore zones

Hi,

the following config fails with knot-resolver 6 because the regex of allow values in subtree is overly strict:

forward:
  - subtree:
      - _tcp.example.org
    servers: [ '10.0.0.11', '10.0.0.12' ]

please consider updating it so that underscore domains can be also forwarded as they have been with knot-resolver before 6.x.

...and here's the output from kresd

Jul 20 15:35:27 test.dns.example.org knot-resolver[43372]: [/] Unexpected value for '<class 'knot_resolver.datamodel.types.types.DomainName'>'. Expected string, got '['_tcp.example.org']' with type '<class 'knot_resolver.utils.modeling.renaming.RenamedList'>'

Regards, Daniel