assistant: When generating a gpg secret key, avoid hardcoding the key algorithm and size

This aims to future-proof gpg key generation. OpenPGP is in flux with a
conflict over standards ongoing. It seems not unlikely that different
systems will have different gpg commands that support different algorithms.

This also simplifies the code by using the --quick-gen-key interface rather
than the experimental batch interface. It seems less likely that
--quick-gen-key will break than an experimental interface (whose
documentation I can no longer find).

--quick-gen-key is supported since gpg 2.1.0 (2014).

Sponsored-by: Graham Spencer on Patreon

Assistant/WebApp/Gpg.hs

@@ -54,7 +54,7 @@ withNewSecretKey :: (KeyId -> Handler Html) -> Handler Html
 withNewSecretKey use = do
 	cmd <- liftAnnex $ gpgCmd <$> Annex.getGitConfig
 	userid <- liftIO $ newUserId cmd
-	liftIO $ genSecretKey cmd RSA "" userid maxRecommendedKeySize
+	liftIO $ genSecretKey cmd "" userid
 	results <- M.keys . M.filter (== userid) <$> liftIO (secretKeys cmd)
 	case results of
 		[] -> giveup "Failed to generate gpg key!"