Ability to push updates to hosting without having all files on disk

[joehinkle11]

A number of developers were using a script to push single file artifacts to hosting. Their script recently broke due to the removal of an internal API it relied on. I happened to need this functionality for a project today and figured it'd take the opportunity to get something into the actual CLI to support this use case.

Link to previous discussion: https://github.com/firebase/firebase-tools/pull/4629#issuecomment-1155638320

It seems most were using this script to avoid having their entire repo in place at the time of running firebase deploy. I'm in a the same boat, I want to be able to save disk space as the content going into hosting grows.

My solution adds a new flag to firebase.json called skip_hash_check_on_empty_file. A better name suggestion would be appreciated.

Example:

{
  "hosting": {
    "skip_hash_check_on_empty_file": true,
    "public": "public",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ]
  }
}

The default value is false. When enabled, the hash check for all empty files will be skipped. This means if you have a 50 mb video called myvideo.mov that you uploaded to hosting, you can then replace that file with an empty one (with the same myvideo.mov). The next time firebase deploy is run, myvideo.mov will be reported to the populateFiles API as having the same hash as the last time it was uploaded.

Updating files still works, as this hash skip only occurs when the file is 0 bytes in length. Deleting files also still works.

Look forward to seeing your thoughts.