feat: Better checks in get_connection

[marcusmunch]

Intent

This PR decreases restriction on host, port, timezone and timezone_out arguments to get_connection.

Approach

From NEWS.md:

• Improved checks on get_connection():
  • If given, host does not need to look like an IP address (e.g. "localhost" is not unrealistic).
  • A character input for port is allowed if it is a string of digits.
  • Now checks if timezone and timezone_out is an IANA time zone.

Known issues

N/A

Checklist

• The PR passes all local unit tests
• I have documented any new features introduced
• If the PR adds a new feature, please add an entry in NEWS.md
• A reviewer is assigned to this PR

[RasmusSkytte]

Looks fine to me