feat(firestore): add support for sum and average aggregated queries

[Lyokone]

Description

Replace this paragraph with a description of what this PR is doing. If you're modifying existing behavior, describe the existing behavior, how this PR is changing it, and what motivated the change.

Related Issues

closes #11848

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.

[larssn]

Any status on this? 😊

Great work btw!

[Lyokone]

Hi @larssn, we are still waiting for an internal API Review to release this. It should come soon. In the mean time, I've updated this branch with master so you can start using it if needed:
pubpec.yaml

  cloud_firestore:
    git:
      url: https://github.com/firebase/flutterfire.git
      path: packages/cloud_firestore/cloud_firestore
      ref: feat/firestore-average-sum

[larssn]

Hi @larssn, we are still waiting for an internal API Review to release this. It should come soon. In the mean time, I've updated this branch with master so you can start using it if needed: pubpec.yaml

  cloud_firestore:
    git:
      url: https://github.com/firebase/flutterfire.git
      path: packages/cloud_firestore/cloud_firestore
      ref: feat/firestore-average-sum

Cool, might try it out, thank you.
However, I can't use it in production until it is officially released.

Fingers crossed it won't be too long. 🤞😊

[Luluch1412]

Hope it is being merged soon.
Actually it is not running on iOS?