Allow specifying WORK_DIR for intermediate files

[mpoberezhniy]

This is required for #234.

Since pre-commit passes --user=<UID:GID> and --workdir=/src - files can not be created at /.

Ran the tests:

...
summary_useful_links.bats
 ✓ summary_useful_links()

87 tests, 0 failures

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 77.27273% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 84.96%. Comparing base (52bab0c) to head (2a59007).

Files	Patch %	Lines
src/index.sh	61.53%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #393      +/-   ##
==========================================
+ Coverage   84.80%   84.96%   +0.15%     
==========================================
  Files           4        4              
  Lines         283      286       +3     
==========================================
+ Hits          240      243       +3     
  Misses         43       43              

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[jamacku]

LGTM, Thank you