Box function import count linter

[radbasa]

Changes

• Closes Box function import count #536
• Adds a box_func_import_count_linter()
• Adds the linter to the .lintr template
• Adds documentation

How to test

1. Unit tests for box_func_import_count_linter() exist.
2. Locally install rhino, version should be 1.6.0.9003, initialize a new rhino application then proceed to declare box imports.
3. rhino::lint_r() should find and point to all function imports that are more than 5 (default) per package/module.
4. Or, with an existing rhino app, add box_trailing_commas_linter = rhino::box_func_import_count_linter() to .lintr.
5. rhino::lint_r() should find and point to all function imports that are more than 5 (default) per package/module.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (db8e2f8) 28.57% compared to head (f3e829e) 31.64%.

❗ Current head f3e829e differs from pull request most recent head 96683d7. Consider uploading reports for the commit 96683d7 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #537      +/-   ##
==========================================
+ Coverage   28.57%   31.64%   +3.07%     
==========================================
  Files          10       10              
  Lines         511      534      +23     
==========================================
+ Hits          146      169      +23     
  Misses        365      365              

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[radbasa]

Change max to 8.

[radbasa]

add a nolint selector to the e2etest app file

[jakubnowicki]

LGTM