feat(mcp): Enhance MCP server capabilities across vector-search tooling + Auth for http scenarios

[anshulkhantwal]

Proposed changes

This PR adds two major enhancements to the MCP server, improving vector-search capabilities for MCP tools, simplifying configuration, and introducing flexible authentication options via Azure Managed Identity.

Key Updates

• Vector Search Tooling: Added two new vector-search variants. The vector-search tool enables semantic similarity queries against MongoDB collections using the $vectorSearch aggregation stage. This feature remains disabled unless a valid embedding configuration is provided.
• Authentication: The HTTP transport now supports pluggable authentication strategies configurable through the httpAuthMode option. A new azure-managed-identity implementation has been added, validating Azure Entra ID (Managed Identity / Service Principal) access tokens supplied via the Authorization: Bearer <token> header.

Checklist

• I have signed the MongoDB CLA