Docs for SERVER-40938: Add tests that dbhash and map-reduce do not accept a read concern

Description

Description:

dbHash and mapReduce do not take {readConcern: {afterClusterTime: ...}} anymore and thus cannot be used in causally consistent sessions. We should probably add these two commands to the list here: https://docs.mongodb.com/manual/core/read-isolation-consistency-recency/#limitations

Engineering Ticket Description:

If they did they could get prepare conflicts which would cause deadlocks.

Scope of changes

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