Sets the umask before executing the task in Docker.

[afourney]

Why are these changes needed?

When code is run in Docker, the output files are owned by root, and may not be manageable by the user who is running Autogen. This PR sets the umask to 000 so that files created in the Testbed's docker environment are world-writable, and can be managed.

Related issue number

Closes #592

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.

[sonichi]

I wanted to confirm whether this is intended for use of pyautogen<0.2 only, and if so, the README needs to state that.

[afourney]

@sonichi Please have another look. I've added version backward compatibility.

The ability to specify other Autogen versions is also in another per #671

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2a96e4d) 34.04% compared to head (095703e) 28.70%.
Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #593      +/-   ##
==========================================
- Coverage   34.04%   28.70%   -5.35%     
==========================================
  Files          25       27       +2     
  Lines        3005     3383     +378     
  Branches      668      760      +92     
==========================================
- Hits         1023      971      -52     
- Misses       1906     2341     +435     
+ Partials       76       71       -5     

Flag	Coverage Δ
unittests	28.64% <ø> (-5.34%)	⬇️

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