Add support for new GH Issue workflow

[scannillo]

Summary of changes

• Add support for new GH issue workflow, which allows for different GH templates for bug reports, feature requests, and contacting support.
• Align with BT Android and iOS on terminology for more granular bug_report.md template details (such as steps to reproduce and screenshots).

See similar PR - https://github.com/braintree/braintree_android/pull/615

Checklist

• ~Added a changelog entry~

Authors

@scannillo

[scannillo]

Hopefully improve the quality and detail in our inbounding issues