terraform-providers.mkProvider: init (#140465)

Expose how the providers are being created. That way, users can more
easily extend or override the list of providers that they want to use.

For example, you need a new AWS provider version:

```nix
terraform.withPlugins (p: [
  (p.mkProvider rec {
    owner = "hashicorp";
    provider-source-address = "registry.terraform.io/hashicorp/aws";
    repo = "terraform-provider-aws";
    rev = "v${version}";
    sha256 = "0fa61i172maanxmxz28mj7mkgrs9a5bs61mlvb0d5y97lv6pm2xg";
    vendorSha256 ="1s22k4b2zq5n0pz6iqbqsf6f7chsbvkpdn432rvyshcryxlklfvl";
    version = "3.56.0";
  })
])
```

pkgs/applications/networking/cluster/terraform-providers/default.nix

@@ -39,25 +39,28 @@ let
       passthru = data;
     };
 
-  # These providers are managed with the ./update-all script
-  automated-providers = lib.mapAttrs (_: attrs:
+  # Our generic constructor to build new providers
+  mkProvider = attrs:
     (if (lib.hasAttr "vendorSha256" attrs) then buildWithGoModule else buildWithGoPackage)
-      attrs) list;
+      attrs;
+
+  # These providers are managed with the ./update-all script
+  automated-providers = lib.mapAttrs (_: attrs: mkProvider attrs) list;
 
   # These are the providers that don't fall in line with the default model
   special-providers = {
     # Packages that don't fit the default model
-    ansible = callPackage ./ansible {};
-    cloudfoundry = callPackage ./cloudfoundry {};
-    gandi = callPackage ./gandi {};
-    hcloud = callPackage ./hcloud {};
-    libvirt = callPackage ./libvirt {};
-    linuxbox = callPackage ./linuxbox {};
-    lxd = callPackage ./lxd {};
-    vpsadmin = callPackage ./vpsadmin {};
-    vercel = callPackage ./vercel {};
+    ansible = callPackage ./ansible { };
+    cloudfoundry = callPackage ./cloudfoundry { };
+    gandi = callPackage ./gandi { };
+    hcloud = callPackage ./hcloud { };
+    libvirt = callPackage ./libvirt { };
+    linuxbox = callPackage ./linuxbox { };
+    lxd = callPackage ./lxd { };
+    vpsadmin = callPackage ./vpsadmin { };
+    vercel = callPackage ./vercel { };
   } // (lib.optionalAttrs (config.allowAliases or false) {
     kubernetes-alpha = throw "This has been merged as beta into the kubernetes provider. See https://www.hashicorp.com/blog/beta-support-for-crds-in-the-terraform-provider-for-kubernetes for details";
   });
 in
-  automated-providers // special-providers
+automated-providers // special-providers // { inherit mkProvider; }

pkgs/applications/networking/cluster/terraform/default.nix

@@ -114,7 +114,7 @@ let
           passthru = {
             withPlugins = newplugins:
               withPlugins (x: newplugins x ++ actualPlugins);
-            full = withPlugins lib.attrValues;
+            full = withPlugins (p: lib.filter lib.isDerivation (lib.attrValues p));
 
             # Ouch
             overrideDerivation = f: