macaroons: reject unknown macaroon versions

We've only ever made macaroons with the v2 versions, so we should
explicitly reject those that aren't actually v2. We add a basic test
along the way, and also add a similar check for the version encoded in
the macaroon ID.

docs/release-notes/release-notes-0.17.1.md

@@ -26,6 +26,8 @@
 * A bug that would cause taproot channels to sometimes not display as active
   [has been fixed](https://github.com/lightningnetwork/lnd/pull/8104).
 
+* [`lnd` will now properly reject macaroons with unknown versions.](https://github.com/lightningnetwork/lnd/pull/8132)
+
 # New Features
 ## Functional Enhancements