what about MongoDB support for workflow persistence store?

# Summary

Add MongoDB support for workflow persistence store

# Use Cases

In my situation，there is a MongoDB cluster already，and we are strongly depend on MongoDB，so I think make MongoDB
support for workflow persistence store is a good idea。Is it meaningful ？

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**Message from the maintainers**:

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Start by reviewing the workflow persistence store and how existing persistence technologies are integrated. Determine the MongoDB design needed for the stated cluster-based use case, including what compatibility and persistence behavior must be covered; done means documented MongoDB support for workflow persistence.

Written by the indexing model from the issue text.