Fix hostname validation for IPv6 hosts

What does this MR do?

Fix hostname validation for IPv6 hosts

The hostname/URL validation currently does in IPv6 environments. IPv6 literals in URLs are enclosed in square brackets.

https://www.rfc-editor.org/rfc/rfc3986#section-3.2.2

Changelog: fixed

Relates gitlab-org/charts/gitlab#2778 (closed)

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
  • Changelog: fixed
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines