Add RegistryLockVerifyAction (#461)

* Add RegistryLockVerifyAction

The action takes two parameters
- isLock is a boolean, determining whether we're trying to lock or
unlock a domain
- lockVerificationCode is the UUID by which we'll look up the lock
object in question.

The lock in question must not be expired and must be in a valid lockable
/ unlockable state

* Some responses to CR

* Add slash and move test method

* Add more data and tests

* Fix screenshot

core/src/test/resources/google/registry/module/frontend/frontend_routing.txt

@@ -6,3 +6,4 @@ PATH                  CLASS                         METHODS  OK AUTH_METHODS
 /registrar-ote-status OteStatusAction               POST     n  API,LEGACY          USER PUBLIC
 /registrar-settings   RegistrarSettingsAction       POST     n  API,LEGACY          USER PUBLIC
 /registry-lock-get    RegistryLockGetAction         GET      n  API,LEGACY          USER PUBLIC
+/registry-lock-verify RegistryLockVerifyAction      GET      n  API,LEGACY          USER PUBLIC