Update AGS (Support Workbenches ++)

[victordibia]

Why are these changes needed?

AG has moved to a workbench model for passing tools to assistant agent (with support for MCP).
This PR updates AGS to support workbench, with some utilities to test MCP and other minor updates.

• Add workbench to Gallery (workbenches are now part of the default gallery)
• Add workbench to team builder UI (you can now drag workbenches to assistant agent in team builder)
• Ability to test MCP server configurations from the workbench (uses the mcp python sdk) . Includes listing capabilities (tools, resources, prompts etc) and testing tool calls in the UI directly.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.27%. Comparing base (8ed8c56) to head (3010433).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6736   +/-   ##
=======================================
  Coverage   80.27%   80.27%           
=======================================
  Files         232      232           
  Lines       17648    17648           
=======================================
  Hits        14167    14167           
  Misses       3481     3481           

Flag	Coverage Δ
unittests	80.27% <ø> (ø)

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