[nix] Revert protoc-gen-grpc-web to 1.4.2 using overlay

Summary:
This creates an overlay with the last nixpkgs revision `9957cd48326fe8dbd52fdc50dd2502307f188b0d` to have grpc-web version 1.4.2
and replaces the dev-shell installation which uses the latest nixpkgs-unstable grpc-web package.

Test Plan: Successfully ran nix develop and it installed 1.4.2 properly

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10739

Author: wyilio

flake.lock

@@ -4,17 +4,22 @@
   inputs = {
     utils.url = "github:numtide/flake-utils";
     nixpkgs-unstable.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    nixpkgs-grpc-web.url = "github:NixOS/nixpkgs/9957cd48326fe8dbd52fdc50dd2502307f188b0d";
     # Do not update, used for EOL versions of mariaDB and arcanist+php8.0
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
   };
 
-  outputs = { self, nixpkgs, nixpkgs-unstable, utils, ... }:
+  outputs = { self, nixpkgs, nixpkgs-grpc-web, nixpkgs-unstable, utils, ... }:
     let
       # Overlays allow for extending a package set, in this case, we are
       # extending nixpkgs with our devShell
       localOverlay = import ./nix/overlay.nix;
+      grpcWebOverlay = final: prev: {
+        protoc-gen-grpc-web = nixpkgs-grpc-web.legacyPackages.aarch64-darwin.protoc-gen-grpc-web;
+      };
       overlays = [
         localOverlay
+        grpcWebOverlay
         (_: _: { commSrc = toString self; } )
       ];