ssh: add generic Match support for matchBlocks (#2992)

* ssh: add generic Match support for matchBlocks

Introduce conservative support for actual `Match`
blocks in ssh config.

"Conservative" means this PR doesn'tt try to process
the `match` expression and simply uses it as a string
provided by the user.

If set, `match` has precedence over `host` meaning
if both are set, `match` is used and `host` is ignored.

* Add news entry

modules/misc/news.nix

@@ -843,6 +843,15 @@ in
             export MOZ_ALLOW_DOWNGRADE=1
         '';
       }
+
+      {
+        time = "2022-11-27T13:14:01+00:00";
+        message = ''
+          'programs.ssh.matchBlocks.*' now supports literal 'Match' blocks via
+          'programs.ssh.matchBlocks.*.match' option as an alternative to plain
+          'Host' blocks
+        '';
+      }
     ];
   };
 }