Add support for Firestore Enterprise Pipeline Queries

[Snargol]

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.