Intercept.v1 hostname should allow underscores

[smilindave26]

tod.burtchell: Hostname format is built-in https://json-schema.org/understanding-json-schema/reference/string.html#hostnames, and references the RFC - https://datatracker.ietf.org/doc/html/rfc952 - which says:

 1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
   to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
   sign (-), and period (.).  Note that periods are only allowed when
   they serve to delimit components of "domain style names"

clint.dovholuk: we want idn-hostname instead newtonsoft also validates it with idn-hostname

"Internationalized label" is used when a term is needed to refer to a
   single label of an IDN, i.e., one that might be any of an NR-LDH
   label, A-label, or U-label.  There are some standardized DNS label
   formats, such as the "underscore labels" used for service location
   (SRV) records \[[RFC2782](https://datatracker.ietf.org/doc/html/rfc2782)\], that do not fall into any of the three
   categories and hence are not internationalized labels.

[dovholuknf]

duplicates https://github.com/openziti/ziti/issues/1119 which might move to this repo since that's where the schema is...