Auto-populate PR description from commit message

[ajryan]

Extends the behavior that auto-populates title when there is a single commit to also copy the entire commit comment to PR description. Resolves #695.

Please make sure the code is following contribution guidelines in CONTRIBUTING.md

• [x] : This PR has a corresponding issue open in the Repository.
• [ ] : Approach is signed off on the issue.

[v-anvashist]

Hi @ajryan We are planning to publish next CLI release.

Can you please assist us here to test this PR?