Add session_id_param to ACADynamicSessionsCodeExecutor

[stuartleeks]

Why are these changes needed?

The initializer for ACADynamicSessionsCodeExecutor creates a new GUID to use as the session ID for dynamic sessions.

In some scenarios it is desirable to be able to re-create the agent group chat from saved state. In this case, the ACADynamicSessionsCodeExecutor needs to be associated with a previous instance (so that any execution state is still valid)

This PR adds a new argument to the initializer to allow a session ID to be passed in (defaulting to the current behaviour of creating a GUID if absent).

Related issue number

Closes #6119

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.

[stuartleeks]

One outstanding question I have is what the behaviour should be if restart is called?

Ideas so far

1. reset the ID to a new GUID (current behaviour)
2. add an optional arg to set a new ID if passed but revert to a new GUID by default
3. add a preserve_session_id arg to __init__ that controls whether the session ID is preserved to reset when calling restart

Would be interested in thoughts :-)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.32%. Comparing base (9de16d5) to head (a4fa448).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6171   +/-   ##
=======================================
  Coverage   77.31%   77.32%           
=======================================
  Files         197      197           
  Lines       13797    13797           
=======================================
+ Hits        10667    10668    +1     
+ Misses       3130     3129    -1     

Flag	Coverage Δ
unittests	77.32% <100.00%> (+<0.01%)	⬆️

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[ekzhu]

Looks like there is a pyright error.

[ekzhu]

I think we can keep the current behavior with a note in the API doc.

.. note: 
  
  The session ID will be reset upon `restart()`. 

We can get feedback later.

One outstanding question I have is what the behaviour should be if restart is called?

Ideas so far

1. reset the ID to a new GUID (current behaviour)
2. add an optional arg to set a new ID if passed but revert to a new GUID by default
3. add a preserve_session_id arg to __init__ that controls whether the session ID is preserved to reset when calling restart

Would be interested in thoughts :-)

[stuartleeks]

Added a note to make the behaviour when calling restart clear. Rebased on latest main