[upload_symbols_to_crashlytics] add support for debug flag

[yangsu]

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

Make it easier to diagnose problems for upload-symbols, particularly in CI environments. Here's an issue I ran into with our pipeline that turned out to be a network proxy configuration problem.

Description

• Added a debug flag for upload_symbols_to_crashlytics with default: false
• When debug is enabled, log upload-symbols output by default
• Added test case that covers the new debug argument and a previously untested path for the platform config value

Testing Steps

I tested this locally and the cryptic message from above turned into this on my local machine

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[yangsu]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[janpio]

Beautiful - thanks!

[fastlane-bot]

Hey @yangsu 👋

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 2.151.0 🚀