modules/borgbackup: migrate to clanServices

Migrates the borgbackup module to clanServices, preserving it's original
configuration syntax and functionality

checks/borgbackup-legacy/default.nix

@@ -0,0 +1,51 @@
+(
+  { ... }:
+  {
+    name = "borgbackup";
+
+    nodes.machine =
+      { self, pkgs, ... }:
+      {
+        imports = [
+          self.clanModules.borgbackup
+          self.nixosModules.clanCore
+          {
+            services.openssh.enable = true;
+            services.borgbackup.repos.testrepo = {
+              authorizedKeys = [ (builtins.readFile ../assets/ssh/pubkey) ];
+            };
+          }
+          {
+            clan.core.settings.directory = ./.;
+            clan.core.state.testState.folders = [ "/etc/state" ];
+            environment.etc.state.text = "hello world";
+            systemd.tmpfiles.settings."vmsecrets" = {
+              "/etc/secrets/borgbackup/borgbackup.ssh" = {
+                C.argument = "${../assets/ssh/privkey}";
+                z = {
+                  mode = "0400";
+                  user = "root";
+                };
+              };
+              "/etc/secrets/borgbackup/borgbackup.repokey" = {
+                C.argument = builtins.toString (pkgs.writeText "repokey" "repokey12345");
+                z = {
+                  mode = "0400";
+                  user = "root";
+                };
+              };
+            };
+            # clan.core.facts.secretStore = "vm";
+            clan.core.vars.settings.secretStore = "vm";
+
+            clan.borgbackup.destinations.test.repo = "borg@localhost:.";
+          }
+        ];
+      };
+    testScript = ''
+      start_all()
+      machine.systemctl("start --wait borgbackup-job-test.service")
+      assert "machine-test" in machine.succeed("BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK=yes /run/current-system/sw/bin/borg-job-test list")
+    '';
+  }
+)