home: introduce ssh module that enables defining multi-proxy targets

also defines some good defaults for ssh.
workmac config already refactored. desktop config tbd.

home/common.nix

@@ -11,6 +11,8 @@
     ./modules/vscodium.nix
     ./modules/fonts.nix
     ./modules/captive-browser.nix
+    ./modules/ensureDirs.nix
+    ./modules/ssh.nix
   ];
   home.homeDirectory =
     if pkgs.stdenv.isDarwin then "/Users/${config.home.username}" else "/home/${config.home.username}";