Use regular expressions to validate tailscale hostname #2714

[FroggyFlox]

Fixes #2714
@Hooverdan96, @phillxnet: ready for review.

Following up on @Hooverdan96's suggestion to leverage regular expressions to better validate the hostname key in the Tailscale service config.

The current mechanism uses a hard-coded list of characters to exclude them from a custom tailscale hostname if present. This is rather ugly and does not scale to all the characters (such as unicode) that need to be excluded.

Switch to using regular expressions to exclude only characters from the hostname that do not belong to that regular expression.

All tests still pass...

buildvm155:/opt/rockstor/src/rockstor # poetry run django-admin test
Creating test database for alias 'default'...
Creating test database for alias 'smart_manager'...
System check identified no issues (0 silenced).
......................................................................................................................................................................................................................................................................................
----------------------------------------------------------------------
Ran 278 tests in 15.039s

OK

... and I was able to configure and turn ON the Tailscale service with a custom hostname being taken in effect (as seen on the Tailscale machines dashboard).

[phillxnet]

@FroggyFlox Thanks for this follow-up. Much appreciated.

RPM built OK with this included so all tests passed via %check scriptlet. And your addition to the test data confirms the added sensitivity and move to inclusion rather than list of chars to exclude.

Web-UI test irrelevant as we already have your prior equivalent character inclusion via the following form validator:

rockstor-core/src/rockstor/storageadmin/static/storageadmin/js/views/configure_service.js

Lines 49 to 52 in ee4af7c

	$.validator.addMethod('isAlphanumericWithHyphens', function(value, element) {
	var regExp = new RegExp(/^[A-Za-z0-9-]+$/);
	return this.optional(element) || regExp.test(value);
	}, 'The hostname can only contain alphanumeric characters or hyphens.')

[FroggyFlox]

Thanks a lot for the review and RPM build testing, @phillxnet.
Given your approval and passing tests, I'll go ahead and merge this.
@Hooverdan96, let me know if you see something needing validation that I missed and I'll create a dedicated PR. I did not think about the unicode characters so thank you very much for bringing it up in your previous review!