Update public name validation to allow upper-case letters

[arash77]

Enhance the public name validation to accept upper-case letters, ensuring a broader range of valid names. Adjusted related error messages accordingly.
Fixes #19087

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[mvdbeek]

Usernames should be lowercase, I don't think a bug in casting them to lowercase should dictate that we now allow this.

[arash77]

So I will just close this PR.