[DOCS]: Add Mastra-Astra Integration Tutorial

[akuya-ekorot]

This PR adds a comprehensive tutorial for integrating Mastra with Astra DB. The tutorial demonstrates:

1. Basic setup of Mastra with Astra DB for semantic recall
2. Enhanced implementation with custom RAG tools

The tutorial follows a progressive approach, showing how to leverage Astra DB's vector capabilities for both automatic memory management and domain-specific data storage.

[calcsam]

@briangodsey -- can we get a PR review on this?

[calcsam]

Mastra + Astra would be v cool :)