[ImportFromJSONAction Plugin] fixed "undefined openmct" bug

[johnriedel]

Closes #7983

Describe your changes:

Simple fix applied using "bind(this)".

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Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
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Reviewer Checklist

• Changes appear to address issue?
• Reviewer has tested changes by following the provided instructions?
• Changes appear not to be breaking changes?
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• Code style and in-line documentation are appropriate?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.30%. Comparing base (5be103e) to head (34a6a32).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7984      +/-   ##
==========================================
- Coverage   57.70%   57.30%   -0.40%     
==========================================
  Files         678      678              
  Lines       27428    27428              
  Branches     2691     2691              
==========================================
- Hits        15826    15718     -108     
- Misses      11264    11370     +106     
- Partials      338      340       +2     

Flag	Coverage Δ
e2e-ci	61.80% <ø> (-1.02%)	⬇️
e2e-full	41.91% <ø> (-0.10%)	⬇️
unit	49.37% <ø> (-0.15%)	⬇️

Files with missing lines	Coverage Δ
...ugins/importFromJSONAction/ImportFromJSONAction.js	76.00% <ø> (ø)

... and 22 files with indirect coverage changes

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