✨ Add new composer-filename option

[badasukerubin]

Description

As discussed in #258 .

This adds a new composer-filename option to the action, allowing for adding a custom composer filename, which can be helpful for using composer based on different environments.

See: https://getcomposer.org/doc/03-cli.md#composer

Fixes #258.

Motivation and context

See: #258

How has this been tested?

Both unit tests as well as integration tests are included with the PR.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.05%. Comparing base (6a168db) to head (a6d8f18).
Report is 1 commits behind head on v3.

Additional details and impacted files

@@            Coverage Diff             @@
##               v3     #261      +/-   ##
==========================================
- Coverage   97.65%   97.05%   -0.60%     
==========================================
  Files           6        6              
  Lines         128      136       +8     
==========================================
+ Hits          125      132       +7     
- Misses          3        4       +1     

Files with missing lines	Coverage Δ
bin/composer_install.sh	100.00% <100.00%> (ø)
bin/composer_paths.sh	97.67% <100.00%> (+0.23%)	⬆️

... and 1 file with indirect coverage changes

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[ramsey]

Thank you for contributing, and sorry for taking so long to review this.

I've made a slight change, using composer-filename instead of custom-composer-filename and setting its default value to "composer". I hope this is okay with you.

[derrabus]

I believe this change broke workflows that used the COMPOSER env variable previously to achieve the same thing, see #264.