Barebones implementation of local builds

[falahat]

Description

Adds some prototype code for building nextjs apps locally.

Scenarios Tested

• I created a firebase.json for a test app with local builds enabled

{
  "apphosting": {
    "backendId": "local-build",
    "rootDir": "/",
    "localBuild": true,
    "ignore": [
      "node_modules",
      ".git",
      "firebase-debug.log",
      "firebase-debug.*.log",
      "functions"
    ]
  }
}

• I enabled the apphostinglocalbuilds flag and tested a local deployment and it was successful. Env vars did not work (as expected) but I was otherwise able to visit the locally built / zip-deployed site.

• I tested a source deploy app

• I disabled the apphostinglocalbuilds flag and the CLI correctly failed my deployment with a clear error message.

Sample Commands

firebase deploy

[falahat]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces barebones support for local builds in App Hosting, allowing the deployment of pre-built artifacts. Key changes include updating dependencies, adding a new createTarArchive utility for packaging local build outputs, and modifying the deployment and release processes to differentiate between source and local build deployments. New test cases have been added to cover the local build functionality and experiment flag enforcement. The documentation for localBuild and the main deployment function has also been improved.

[falahat]

I manually tested a local build and it was correctly deployed. Of course, env vars didn't work yet but I confirmed that:

1. We didn't do a Cloud Build for this deployment
2. The rollout (from CLI) was successful and I saw the new version/rollout on the Firebase Console
3. I was able to use the deployed nextjs site