Add agent robot example to gallery

[AaronWard]

Adding the example of using autogen as a brain for a robot to the gallery

Why are these changes needed?

Requested by @sonichi to add to the gallery

Related issue number

#1239

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation 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-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9708058) 39.46% compared to head (8b52445) 39.46%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1718   +/-   ##
=======================================
  Coverage   39.46%   39.46%           
=======================================
  Files          57       57           
  Lines        6020     6020           
  Branches     1346     1346           
=======================================
  Hits         2376     2376           
  Misses       3449     3449           
  Partials      195      195           

Flag	Coverage Δ
unittests	39.46% <ø> (ø)

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[rickyloynd-microsoft]

Great addition!