Update feature matrix for Astra DB vector store integration

[sl-at-ibm]

Overview

This PR updates the feature matrix for the Astra DB vector store integration.

Type of change

Type: Update existing documentation

Checklist

• I have read the contributing guidelines
• [?] I have tested my changes locally using docs dev
• [n/a] All code examples have been tested and work correctly
• [n/a] I have used root relative paths for internal links
• [n/a] I have updated navigation in src/docs.json if needed
• I have gotten approval from the relevant reviewers

Additional notes

This PR marks these two attributes as "yes" for the Astra DB Vector Store component: passes standard tests and multi tenancy.

For the first item, the component uses the entire vectorstore suite from the langchain-tests in its CI/CD and passes it.

For the multi-tenancy, Astra DB is a cloud database: as such, is it my understanding that it is inherently multitenant, as each user comes with their own auth token and accesses their own databases there through DB-specific endpoints (see e.g. here). In that respect, it is not different than e.g. the Mongo DB Atlas vector store, likewise marked as multitenant in the feature matrix.