opentofu: Allow using terraform-providers.* from binary cache

Currently `opentofu.withPlugins(p: [p.<plugin>])` causes `<plugin>` to
rebuild.

Since we build terraform-providers.* from source, overriding homepage
of terraform-providers.* only affects their `postInstall` phase, the
providers binaries remain the same.

We can avoid the provider rebuilds by creating the right dir in the
wrapper.

pkgs/by-name/op/opentofu/package.nix

@@ -108,28 +108,7 @@ let
   withPlugins =
     plugins:
     let
-      actualPlugins = lib.lists.map (
-        provider:
-        if provider ? override then
-          # use opentofu plugin registry over terraform's
-          provider.override (
-            oldArgs:
-            if (builtins.hasAttr "homepage" oldArgs) then
-              {
-                provider-source-address =
-                  lib.replaceStrings
-                    [ "https://registry.terraform.io/providers" ]
-                    [
-                      "registry.opentofu.org"
-                    ]
-                    oldArgs.homepage;
-              }
-            else
-              { }
-          )
-        else
-          provider
-      ) (plugins package.plugins);
+      actualPlugins = plugins package.plugins;
 
       # Wrap PATH of plugins propagatedBuildInputs, plugins may have runtime dependencies on external binaries
       wrapperInputs = lib.unique (
@@ -183,13 +162,16 @@ let
           passthru = package.passthru // passthru;
 
           buildCommand = ''
-            # Create wrappers for terraform plugins because Terraform only
+            # Create wrappers for terraform plugins because OpenTofu only
             # walks inside of a tree of files.
+            # Also replace registry.terraform.io dir with registry.opentofu.org,
+            # so OpenTofu can find the plugins.
             for providerDir in ${toString actualPlugins}
             do
               for file in $(find $providerDir/libexec/terraform-providers -type f)
               do
                 relFile=''${file#$providerDir/}
+                relFile=''${relFile/registry.terraform.io/registry.opentofu.org}
                 mkdir -p $out/$(dirname $relFile)
                 cat <<WRAPPER > $out/$relFile
             #!${runtimeShell}