Update Costing Doc Automation

[MarcusHolly]

Summary/Motivation:

In the unit model costing documentation there was a column named "Default Value" under the Costing Method Variables section. Since this column does not make sense for many of these variables, this column has been changed to "Index". This PR also changes the variable and parameter names to the monospacing font to distinguish them from regular text.

Changes proposed in this PR:

• "Default Value" column changed to "Index" in unit model costing documentation template
• Variable and Parameter names changed to monospacing font in unit model costing documentation template
• Updates existing unit model costing documentation to use monospacing font for Vars and Params

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.
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[agarciadiego]

LGTM

[hunterbarber]

@MarcusHolly I think you're the author of all the existing cost docs in main as of now which already have this change applied?

[MarcusHolly]

@MarcusHolly I think you're the author of all the existing cost docs in main as of now which already have this change applied?

I also didn't touch documentation that are currently in open PRs (GAC, Electrolyzer, and crystallizer), but those all adhere to this format now as well

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.02%. Comparing base (f8a9e29) to head (c527812).
Report is 58 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1394   +/-   ##
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  Coverage   94.02%   94.02%           
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  Files         335      335           
  Lines       35620    35620           
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  Hits        33491    33491           
  Misses       2129     2129           

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