fix(parameters): appconfig internal _get docstrings

[ran-isenberg]

Issue #, if available: NA

Description of changes:

fix _get of appconfig parameter utility documentation

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

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[codecov-commenter]

Codecov Report

Merging #934 (3f8d60f) into develop (22f8719) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #934   +/-   ##
========================================
  Coverage    99.96%   99.96%           
========================================
  Files          118      118           
  Lines         5291     5291           
  Branches       608      608           
========================================
  Hits          5289     5289           
  Partials         2        2           

Impacted Files	Coverage Δ
...ambda_powertools/utilities/parameters/appconfig.py	100.00% <ø> (ø)

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