Improve MongoDB read model repopulation performance via BulkWriteAsync

[Fariarx]

Changes:

• Replaced sequential ReplaceOneAsync calls with BulkWriteAsync in UpdateAsync method when processing multiple (>1) read model updates

Impact:
Significantly accelerates read model repopulation in MongoDB.​

Production proven:
This change has been running in production for over a year with excellent stability and 2-4x performance improvement for batches >1000 events during repopulation.

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