Support GIT_SSH and GIT_SSH_COMMAND

They are handled close the same as they are by git. However, unlike git,
git-annex sometimes needs to pass the -n parameter when using these.

So, this has the potential for breaking some setup, and perhaps there ought
to be a ANNEX_USE_GIT_SSH=1 needed to use these. But I'd rather avoid that
if possible, so let's see if anyone complains.

Almost all places where "ssh" was run have been changed to support the env
vars. Anything still calling sshOptions does not support them. In
particular, rsync special remotes don't. Seems that annex-rsync-transport
already gives sufficient control there.

(Fixed in passing: Remote.Helper.Ssh.toRepo used to extract
remoteAnnexSshOptions and pass them to sshOptions, which was redundant
since sshOptions also extracts those.)

This commit was sponsored by Jeff Goeke-Smith on Patreon.

Command/Map.hs

@@ -224,10 +224,10 @@ tryScan r
 		(pipedconfig, return Nothing) "configlist" [] []
 	manualconfiglist = do
 		gc <- Annex.getRemoteGitConfig r
-		sshparams <- Ssh.toRepo NoConsumeStdin r gc [Param sshcmd]
-		liftIO $ pipedconfig "ssh" sshparams
+		(sshcmd, sshparams) <- Ssh.toRepo NoConsumeStdin r gc remotecmd
+		liftIO $ pipedconfig sshcmd sshparams
 	  where
-		sshcmd = "sh -c " ++ shellEscape
+		remotecmd = "sh -c " ++ shellEscape
 			(cddir ++ " && " ++ "git config --null --list")
 		dir = Git.repoPath r
 		cddir