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.

Types/Remote.hs

@@ -60,7 +60,7 @@ data RemoteTypeA a = RemoteType
 	-- generates a remote of this type
 	, generate :: Git.Repo -> UUID -> ParsedRemoteConfig -> RemoteGitConfig -> RemoteStateHandle -> a (Maybe (RemoteA a))
 	-- parse configs of remotes of this type
-	, configParser :: [RemoteConfigParser]
+	, configParser :: a RemoteConfigParser
 	-- initializes or enables a remote
 	, setup :: SetupStage -> Maybe UUID -> Maybe CredPair -> RemoteConfig -> RemoteGitConfig -> a (RemoteConfig, UUID)
 	-- check if a remote of this type is able to support export

Types/RemoteConfig.hs

@@ -37,4 +37,15 @@ data RemoteConfigValue where
  - Presence of fields that are not included in this list will cause
  - a parse failure.
  -}
-type RemoteConfigParser = (RemoteConfigField, Maybe (ProposedAccepted String) -> RemoteConfig -> Either String (Maybe RemoteConfigValue))
+type RemoteConfigFieldParser = (RemoteConfigField, Maybe (ProposedAccepted String) -> RemoteConfig -> Either String (Maybe RemoteConfigValue))
+
+data RemoteConfigParser = RemoteConfigParser
+	{ remoteConfigFieldParsers :: [RemoteConfigFieldParser]
+	, remoteConfigRestPassthrough :: Bool
+	}
+
+mkRemoteConfigParser :: Monad m => [RemoteConfigFieldParser] -> m RemoteConfigParser
+mkRemoteConfigParser l = pure (RemoteConfigParser l False)
+
+addRemoteConfigParser :: [RemoteConfigFieldParser] -> RemoteConfigParser -> RemoteConfigParser
+addRemoteConfigParser l rpc = rpc { remoteConfigFieldParsers = remoteConfigFieldParsers rpc ++ l }