Firestore Aggregation

Here is a micro task;

Create a Firestore collection with some dummy data.
For example create 20 dummy documents that has

A string,
A number,
A date,
An array that has at least 3 keywords.

Aggregate this collection with a cloud function into documents of keywords. Use same keywords for some of the documents to show the aggregation. Lets say 3 documents in this collection has banana keyword in the array. The banana document would be aggregated from 3 documents.
(triggers onCreate, onUpdate, onDelete, onWrite) and updates the aggregated documents or create new ones.

Show one of these aggregated document in a Flutter (or Flutter web) listview.builder as cards.