[DOCS] Additional top-level section highlighting strands-evals

[poshinchen]

Documentation Section

https://github.com/strands-agents/docs/blob/main/mkdocs.yml

Current State

Currently the Strands-evals SDK are in its own section (sdiebar), it will be better to make Strands-evals SDK as its own top-level tab to have visibility.

Suggested Improvement

To have Strands-evals SDK be its own top-level tab to have visibility.

Rationale

For visibility

Additional Context

No response