Validate tenant IDs

[bboreham]

Some restrictions on tenant IDs are documented but not enforced.

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[pracucci]

We're currently validating it when multiple tenant IDs are specified (query federation) but not for the normal use case of a single tenant specified in the request.

[bboreham]

\ and / were disallowed by #4375

Whitespace is still documented as unsupported but allowed by the code.

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.