[docs] No detailed information on Firestore triggers `*WithAuthContext()`

### Related issues

none.

### [REQUIRED] Version info

**node:**
all

**firebase-functions:**
- onDocumentCreatedWithAuthContext
- onDocumentDeletedWithAuthContext
- onDocumentUpdatedWithAuthContext
- onDocumentWrittenWithAuthContext

### [REQUIRED] Test case

Search the Firebase Documentation website. There is only mention of any of the above functions with no detailed reference.

### [REQUIRED] Steps to reproduce

See Test Case section above.

### [REQUIRED] Expected behavior

Documentation for these should exist and be discoverable.

### [REQUIRED] Actual behavior

No documentation exist beyond mention of the functions [in this page](https://firebase.google.com/docs/functions/firestore-events?gen=2nd#function_triggers)

### Were you able to successfully deploy your functions?

N/A