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

hscontrol/mapper/tail.go

@@ -93,7 +93,7 @@ func tailNode(
 		User: tailcfg.UserID(node.UserID),
 
 		Key:       node.NodeKey,
-		KeyExpiry: keyExpiry,
+		KeyExpiry: keyExpiry.UTC(),
 
 		Machine:    node.MachineKey,
 		DiscoKey:   node.DiscoKey,
@@ -102,7 +102,7 @@ func tailNode(
 		Endpoints:  node.Endpoints,
 		DERP:       derp,
 		Hostinfo:   node.Hostinfo.View(),
-		Created:    node.CreatedAt,
+		Created:    node.CreatedAt.UTC(),
 
 		Online: node.IsOnline,