refactor flake

* switched from flake-utils to flake-parts
* dropped the overlay and instead populate configurable options for all
required authentik components in the module
* `nixosModule.default` is now a top-level output following the flake spec,
instead of the previously incorrect system-specific definition

flake.lock

@@ -17,6 +17,24 @@
         "type": "github"
       }
     },
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1687762428,
+        "narHash": "sha256-DIf7mi45PKo+s8dOYF+UlXHzE0Wl/+k3tXUyAoAnoGE=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "37dd7bb15791c86d55c5121740a1887ab55ee836",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "locked": {
         "lastModified": 1676283394,
@@ -71,6 +89,24 @@
         "type": "github"
       }
     },
+    "nixpkgs-lib": {
+      "locked": {
+        "dir": "lib",
+        "lastModified": 1685564631,
+        "narHash": "sha256-8ywr3AkblY4++3lIVxmrWZFzac7+f32ZEhH/A8pNscI=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4f53efe34b3a8877ac923b9350c874e3dcd5dc0a",
+        "type": "github"
+      },
+      "original": {
+        "dir": "lib",
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "poetry2nix": {
       "inputs": {
         "flake-utils": [
@@ -97,6 +133,7 @@
     "root": {
       "inputs": {
         "authentik-src": "authentik-src",
+        "flake-parts": "flake-parts",
         "flake-utils": "flake-utils",
         "napalm": "napalm",
         "nixpkgs": "nixpkgs",