chore: Modified bug issue template to add checkbox to report potential regression.

[ashishdhingra]

• Modified bug issue template to add checkbox to report potential regression.
• Added GitHub action to add/remove label potential-regression when issue is created/edited.

NOTE:

• The GitHub action code was ported from CDK repo.
• The label potential-regression would need to be created manually (we could use color #FF6700 and description Marking this issue as a potential regression to be checked by team member to make it consistent across SDK repos)

Label potential-regression would make issue standout in the list and help engineers to triage potential high severity issues effectively.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

1. To make sure we include your contribution in the release notes, please make sure to add description entry for your changes in the "unreleased changes" section of the CHANGELOG.md file (at corresponding gem). For the description entry, please make sure it lives in one line and starts with Feature or Issue in the correct format.

2. For generated code changes, please checkout below instructions first:
   https://github.com/aws/aws-sdk-ruby/blob/version-3/CONTRIBUTING.md

Thank you for your contribution!