[snapshot] Add -testPlan option from scan

[jhandguy]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

To allow more flexibility on which tests to run while capturing screenshots, we need to leverage the -testPlan options that already exists in scan.

Description

This change brings the option -testPlan from scan to snapshot.
The snapshot implementation is extremely similar, if not identical, to the scan implementation.

Testing Steps

I have tested this change in my project and I was able to create a retrying mechanism, that only do so with failing tests.

[fastlane-bot]

Hey @jhandguy 👋

Thank you for your contribution to fastlane and congrats on getting this pull request merged 🎉
The code change now lives in the master branch, however it wasn't released to RubyGems yet.
We usually ship about once a week, and your PR will be included in the next one.

Please let us know if this change requires an immediate release by adding a comment here 👍
We'll notify you once we shipped a new release with your changes 🚀

[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.147.0 🚀