Fix webfinger retries (#4275)

* Do not raise unretryable exceptions in ResolveRemoteAccountService

* Removed fatal exceptions from ResolveRemoteAccountService

Exceptions that cannot be retried should not be raised. New exception
class for those that can be retried (Mastodon::UnexpectedResponseError)

app/services/subscribe_service.rb

@@ -18,7 +18,7 @@ class SubscribeService < BaseService
     else
       # The response was either a 429 rate limit, or a 5xx error.
       # We need to retry at a later time. Fail loudly!
-      raise "Subscription attempt failed for #{@account.acct} (#{@account.hub_url}): HTTP #{@response.code}"
+      raise Mastodon::UnexpectedResponseError, @response
     end
   end