chore(fwtools): handle existing resolutions in tarsync

[jtoar]

Currently there's a @graphql-codegen package in canary that doesn't exist at the published version we have to set a resolution for (see dotansimha/graphql-code-generator#9808). yarn rwfw project:tarsync overwrites the resolutions, so you have to add it back after running the command which is annoying. This just makes it add the tarball resolutions to the existing ones:

  "resolutions": {
    // This is now preserved
    "@graphql-codegen/visitor-plugin-common": "4.0.1",
    "@redwoodjs/fastify-plugin-streaming": "./tarballs/redwoodjs-fastify-plugin-streaming.tgz",
    "@redwoodjs/api": "./tarballs/redwoodjs-api.tgz",
    "@redwoodjs/api-server": "./tarballs/redwoodjs-api-server.tgz",
    // ...
  }