feat: parallel delete vector

[miendinh]

Summary

Speed up clean vector by node_id

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• This change requires a documentation update, included: Dify Document
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• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
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[bowenliang123]

-1.

The granularity of delete_by_id is single, too small for deletion, which would cause much more overhead RTT time in calling vdb deletion.

Would you like to do the followings:

1. split all the ids in to bathes
2. execute deletion in parallel with delete_by_ids , the batch deletion
3. make the concurrent number configurable
4. share the singleton thread pool to prevent overuse in opening threads