Summary

This pull request adds the update operation to the vector store nodes.
To implement the update operation user needs to specify the ID of an existing embedding.

Important to note:

1. Update operation could not be implemented the same way as insert operation. It requires input items to correspond 1-1 with the vector store entry (otherwise "update item by ID" operation would make little sense). This is why the vector store node in update mode doesn't have DocumentLoader input and do not split input into chunks.
2. It uses LangChain VectorStore's upsert feature under the hood. Of the n8n vector store nodes only Pinecone and Supabase had upsert feature implemented so far.
3. Update mode is disabled by default for new vector store integrations, it should be enabled case by case (i.e. when the vector store provider has upsert implemented in langchain).

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/AI-202/add-update-operations-to-vector-store-nodes
Docs: n8n-io/n8n-docs#2245

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)