* Fix KeyExpiration when a zero time value has a timezone
When a zero time value is loaded from JSON or a DB in a way that
assigns it the local timezone, it does not roudtrip in JSON as a
value for which IsZero returns true. This causes KeyExpiry to be
treated as a far past value instead of a nilish value.
See https://github.com/golang/go/issues/57040
* Fix whitespace
* Ensure that postgresql is used for all tests when env var is set
* Pass through value of HEADSCALE_INTEGRATION_POSTGRES env var
* Add option to set timezone on headscale container
* Add test for registration with auth key in alternate timezone
