Add support for Firestore Enterprise Pipeline Queries

Firestore has recently launched Pipeline operations in Enterprise edition.
These powerful queries allow for complex transformations, aggregations, and
filtering that go beyond what Core operations currently support.

It would be beneficial for AngularFire to provide wrappers
for Pipeline operations to maintain parity with the Firestore JS SDK and
provide a better Angular developer experience.

In my opinion, the ability to perform searches using regex is the most important feature.

Has a date already been set for implementation?

Thanks for your work.

首先檢視 AngularFire 現有的 Firestore wrapper，以及 Firestore JS SDK 的 Enterprise Pipeline Queries API。確認支援的 Pipeline 操作，包括正規表示式搜尋，然後定義實現與 Angular 對等所需的 wrapper 介面；完成的標準是已公開支援的操作，並由適當的測試涵蓋。

由索引模型根據 Issue 內容生成。