convert configParser to Annex action and add passthrough option

Needed so Remote.External can query the external program for its
configs. When the external program does not support the query,
the passthrough option will make all input fields be available.

Creds.hs

@@ -1,6 +1,6 @@
 {- Credentials storage
  -
- - Copyright 2012-2014 Joey Hess <id@joeyh.name>
+ - Copyright 2012-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -30,7 +30,7 @@ import Utility.FileMode
 import Crypto
 import Types.Remote (RemoteConfig, RemoteConfigField)
 import Types.ProposedAccepted
-import Remote.Helper.Encryptable (remoteCipher, remoteCipher', embedCreds, EncryptionIsSetup, extractCipher, encryptionConfigParser)
+import Remote.Helper.Encryptable (remoteCipher, remoteCipher', embedCreds, EncryptionIsSetup, extractCipher, parseEncryptionConfig)
 import Utility.Env (getEnv)
 
 import qualified Data.ByteString.Lazy.Char8 as L
@@ -79,8 +79,7 @@ setRemoteCredPair encsetup c gc storage mcreds = case mcreds of
 	storeconfig creds key Nothing =
 		return $ M.insert key (Accepted (toB64 $ encodeCredPair creds)) c
 	
-	pc = either (const mempty) id
-		(parseRemoteConfig c encryptionConfigParser)
+	pc = either (const mempty) id (parseEncryptionConfig c)
 
 {- Gets a remote's credpair, from the environment if set, otherwise
  - from the cache in gitAnnexCredsDir, or failing that, from the