Fix "KnowledgeBase.load()" recreates database regardless of param "recreate"

[GuanYixuan]

The method KnowledgeBase.load now recreates the vector database (and discards contents) regardless of the recreate parameter, which does not follow its signature:

def load(self, recreate: bool = False, upsert: bool = False, skip_existing: bool = True) -> None:
    ...

    if recreate:
        logger.info("Deleting collection")
        self.vector_db.delete()

    logger.info("Creating collection")
    self.vector_db.create()

    ...

Therefore this patch aims to fix this, as well as the same "always recreating" behavior in KnowledgeBase.load_documents