feat: Add hostname label validation tag

[KytnaCode]

Fixes Or Enhances

Add hostname_label validation tag. Resolves #1543.

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@go-playground/validator-maintainers

[KytnaCode]

The hostname label rule uses local isDigit and isLetter functions that use ascii ranges for efficiency, I can change alpha, alphanum, alphaspace and alphanumspace to use them instead of regex, although, that doesn't work for unicode variants. I can open a pull request for that, what do you think?.