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/general_test.go

@@ -215,6 +215,14 @@ func TestAuthKeyLogoutAndRelogin(t *testing.T) {
 }
 
 func TestEphemeral(t *testing.T) {
+	testEphemeralWithOptions(t, hsic.WithTestName("ephemeral"))
+}
+
+func TestEphemeralInAlternateTimezone(t *testing.T) {
+	testEphemeralWithOptions(t, hsic.WithTestName("ephemeral-tz"), hsic.WithTimezone("America/Los_Angeles"))
+}
+
+func testEphemeralWithOptions(t *testing.T, opts ...hsic.Option) {
 	IntegrationSkip(t)
 	t.Parallel()
 
@@ -227,7 +235,7 @@ func TestEphemeral(t *testing.T) {
 		"user2": len(MustTestVersions),
 	}
 
-	headscale, err := scenario.Headscale(hsic.WithTestName("ephemeral"))
+	headscale, err := scenario.Headscale(opts...)
 	assertNoErrHeadscaleEnv(t, err)
 
 	for userName, clientCount := range spec {