Make exporting of PyROS subproblems more customizable

[shermanjasonaf]

Summary/Motivation:

The PyROS solver provides two optional arguments keepfiles and subproblem_file_directory for specifying whether and where subproblems that were not solved to an acceptable level are to be written. However, when subproblems are written, they are exclusively written in 'bar' format. Other formats ('gams', 'nl', etc.) may be of interest to the user.

Changes proposed in this PR:

• Add a new optional PyROS solver argument subproblem_format_options. This argument should be (castable to) a dict object, of which each entry maps a Pyomo WriterFactory format (e.g., 'bar', 'gams') to a value for the argument io_options to BlockData.write().
• Add tests to check that PyROS writes subproblems as expected.

TODO (after #3646 merged)

• Update version number, changelog

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.07%. Comparing base (14a1c10) to head (425e76c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3649   +/-   ##
=======================================
  Coverage   89.06%   89.07%           
=======================================
  Files         890      890           
  Lines      102700   102696    -4     
=======================================
+ Hits        91471    91472    +1     
+ Misses      11229    11224    -5     

Flag	Coverage Δ
builders	26.64% <33.33%> (+<0.01%)	⬆️
default	85.66% <100.00%> (?)
expensive	34.00% <33.33%> (?)
linux	86.84% <100.00%> (-1.98%)	⬇️
linux_other	86.84% <100.00%> (+0.03%)	⬆️
osx	83.13% <100.00%> (+0.03%)	⬆️
win	85.02% <100.00%> (+0.02%)	⬆️
win_other	85.02% <100.00%> (+0.02%)	⬆️

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[mrmundt]

I love reductions of duplicate code. Looks good!

[jsiirola]

@shermanjasonaf: Both dependent PRs (#3558 & #3646) have been merged. Once the version # and changelog have been updated, we can merge this one as well.