vectorstores: add Replacement option

[creeper12356]

vectorstores: add Replacement option

This PR introduce a Replacement member to the vectorstores options. This option can be used in AddDocuments function.
When Replacement is set to true, AddDocuments function will delete old record with the same Metadata attribute. (i.e to replace).
When Replacement is set to false (default case) , AddDocuments
function will simply add documents without checking existing
document records.

PR Checklist

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