Firestore: Add test that verifies aggregate query error message when missing index

[dconeybe]

This verifies that the descriptive error message that occurs when the server does not have the required index has the URL that customers can follow to create the index.

This is a port of the "getCountFromServer error message is good if missing index" integration test from https://github.com/firebase/firebase-js-sdk/blob/42bfb0b8243a6c36b66a0bbedf61436e70591062/packages/firestore/test/integration/api/aggregation.test.ts#L130-L155 and firebase/firebase-android-sdk#4232.

Googlers see b/254063570 for details.

#no-changelog

[google-oss-bot]

Coverage Report ¹

Affected Products

• FirebaseFirestore-iOS-FirebaseFirestoreInternal.framework

  Overall coverage changed from 88.16% (9f8909a) to 88.07% (6523ae7) by -0.09%.

  Filename	Base (9f8909a)	Merge (6523ae7)	Diff
  exception.cc	84.21%	23.68%	-60.53%
  filesystem_posix.cc	81.82%	79.09%	-2.73%
  leveldb_key.cc	98.14%	98.82%	+0.69%
  leveldb_remote_document_cache.cc	96.55%	94.83%	-1.72%
  ordered_code.cc	94.39%	93.90%	-0.49%

Test Logs

• Base (9f8909a): https://github.com/firebase/firebase-ios-sdk/actions/runs/7212526367
• Merge (6523ae7): https://github.com/firebase/firebase-ios-sdk/actions/runs/7214338202

1. https://storage.googleapis.com/firebase-sdk-metric-reports/KNBuQ476KN.html

[google-oss-bot]

Size Report ¹

Affected Products

• FirebaseFirestore

  Type	Base (9f8909a)	Merge (6523ae7)	Diff
  CocoaPods	-51.5 kB	-51.5 kB	-1 B (+0.0%)

Test Logs

• Base (9f8909a): https://github.com/firebase/firebase-ios-sdk/actions/runs/7212526367
• Merge (6523ae7): https://github.com/firebase/firebase-ios-sdk/actions/runs/7214338202

1. https://storage.googleapis.com/firebase-sdk-metric-reports/vYr4DW9Ne6.html

[milaGGL]

LGTM!

[milaGGL]

LGTM