Add config to add / remove prefix from report files

[EnricoMi]

Test result files report the file name where test cases are defined. This file name is used to link annotations with the files in the git repository. Some test runners report absolute paths or paths that are not relative to the git repository root.

Those filenames have to be corrected by adding or removing a prefix path.

#35 (comment)

Examples:

publish-unit-test-result-action/python/test/files/mocha/tests.json

Line 41 in d2532d3

"file": "/home/runner/work/mocha/mocha/test/unit/runner.spec.js",

The /home/runner/work/mocha/mocha/ prefix should be removed to make the annotation link to the repository file.

[EnricoMi]

This has been released.