Clarifies the phrasing in notebook agent_hierarchy_flow_using_select_speaker

[joshkyh]

Why are these changes needed?

Improves on the phrasing "information flow" because agents do see the full context of what was previously discussed. It is therefore, not a limitation of information flow, but a limitation on the transition paths.

Related issue number

Clarifies #853
#853 (comment)

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 (a107233) 26.63% compared to head (da4c37c) 26.63%.

Additional details and impacted files

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##             main     #876   +/-   ##
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  Coverage   26.63%   26.63%           
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  Files          28       28           
  Lines        3725     3725           
  Branches      847      847           
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  Hits          992      992           
  Misses       2660     2660           
  Partials       73       73           

Flag	Coverage Δ
unittests	26.57% <ø> (ø)

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