Added support for exporting gradle output to file

[angelolloqui]

Checklist

• I've read and followed the Contribution Guidelines
• step.yml and README.md is updated with the changes (if needed)

Version

Requires a MAJOR/MINOR/PATCH version update

Context

This PR adds support to gradle runner for outputing the raw logs into a file. It is useful if you want to add steps in your workflow that parses the build log searching for specific info.

Resolves: https://discuss.bitrise.io/t/allow-output-from-gradle-runner-step-to-be-stored-in-a-file/22551

Changes

• Added a new input parameter called export_gradle_log as bool
• Make a new case for when export_gradle_log is true, to use a new command helper to write in file
• Created the new command helper that prints the log (full) in console and writes the file
• Updated documentation

Investigation details

Decisions

I decided to leave the parameter as optional and show the full output (instead of last 20 lines like in debug) to keep backward compatibility