[CX] Queue queries during initial connection/rollback

As of DP2, Queries on connected bucket can be run even when the shadows are going through initial sync phase or handling rollbacks.

This behavior is dangerous as it may lead to incorrect results by large margins. Moreover, there is no warning of any kind that the results contain missing information.

To better handle this, DP3 will not allow queries to run on connected buckets during the initial connection phase and during handling of rollbacks. Instead, queries will be queued until initial sync is complete.

How to test this?

1. Connect a bucket.
2. Submit a query on the same bucket from another thread.
3. The query result should not return until the connect statement return.
4. The query result should be correct as of the connect point in time or later.