Add chart options to fsapi

[MichaelPesce]

Fixes/Resolves:

• addresses UI issue #110

Summary/Motivation:

• allows for developers to inform the UI which variables to use for which chart types

Changes proposed in this PR:

• add chart_type and chart_group to ModelExport class

Legal Acknowledgement

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1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
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 94.01%. Comparing base (3d42a54) to head (56c268b).
Report is 49 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1413   +/-   ##
=======================================
  Coverage   94.01%   94.01%           
=======================================
  Files         335      335           
  Lines       35570    35572    +2     
=======================================
+ Hits        33442    33444    +2     
  Misses       2128     2128           

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[adam-a-a]

LGTM!