treewide: add missing systemd ordering directives

In particular, we were missing `sops-install-secrets.service` in a ton
of places, and `network-online.target` for some homebrewn services.

This has caused failure of some services on machine startup.

hosts/bicep/services/git-mirrors/default.nix

@@ -20,6 +20,8 @@ in
       lfs = false;
     };
 
+    # TODO: add a module setting to specify additional systemd dependencies
+    #       and then mark "sops-install-secrets.service" as a dependency here
     instances = let
       defaultGithubConfig = {
         settings.token_file = config.sops.secrets."gickup/github-token".path;