Fix 764 (#2093)

* 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

integration/scenario.go

@@ -249,6 +249,10 @@ func (s *Scenario) Headscale(opts ...hsic.Option) (ControlServer, error) {
 		return headscale, nil
 	}
 
+	if usePostgresForTest {
+		opts = append(opts, hsic.WithPostgres())
+	}
+
 	headscale, err := hsic.New(s.pool, s.network, opts...)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create headscale container: %w", err)
@@ -465,10 +469,6 @@ func (s *Scenario) CreateHeadscaleEnv(
 	tsOpts []tsic.Option,
 	opts ...hsic.Option,
 ) error {
-	if usePostgresForTest {
-		opts = append(opts, hsic.WithPostgres())
-	}
-
 	headscale, err := s.Headscale(opts...)
 	if err != nil {
 		return err