[Enh]: Time to update the SqlClient driver

## What?

The latest stable SqlClient is `7.0.0`.

DAB is using `5.2.3` which is 2 major versions behind.

## Why?

1. Leaner, modular architecture. 7.0 was rewritten to be more lightweight with reduced dependencies
2. Improved OpenIdConnect/Entra ID authentication support which will matter to MCP soon!
3. Enhanced connection resiliency and retry logic. Just makes it all better.
4. TDS 8.0 protocol support for stricter encryption
5. Performance improvements across connection pooling and query execution
6. Security patches accumulated over two major versions

## Potential risks

1. Major version bumps (5 → 6 → 7) typically include breaking changes in API surface, connection string behavior, and default encryption settings. It should be okay, but this will require some testing and research to be sure.
2. SqlClient 6.0+ changed default encryption to `Mandatory`, which might break connections, but we can account for it
3. DAB's codebase has a note reminding devs to update scripts/notice-generation.ps1 when changing this package, suggesting there are known downstream impacts