Add `coverage-reporter-platform` input option

[afinetooth]

Fixes #218

Description

Since we have added support for coverage-reporter on aarch64, we need to provide users of our github-action the ability to select this architecture-specific version of coverage-reporter when on an aarch64 / arm64 runner.

To Do

• [x] New input option - Add coverage-reporter-platform input option to control which architecture-specific version of coverage-reporter is downloaded and run by the github-action. (Linux only.)
• [x] Exception messages - Since this option is not available for MacOS or Windows, we will deliver warning messages if the option is set, but continue processing with default behavior.
  • [x] We have also stepped back from the previous implementation of the exception for coverage-reporter-version on MacOS and have turned that error message + exit code 1 into a warning message, allowing processing to proceed.
• [x] Tests - We have also added tests to test different values for coverage-reporter-platform.