Added upgrade scenario checkbox in PR template

[UtkarshBhatthere]

Description

Added upgrade scenario checkbox to the PR template.

Fixes # NA

Type of change

• [X] Documentation update (Doc only change)

How Has This Been Tested?

Existing CI

Contributor's Checklist

Please check that you have:

• [X] self-reviewed the code in this PR.
• [ ] added code comments, particularly in hard-to-understand areas.
• [ ] updated the user documentation with corresponding changes.
• [ ] added tests to verify effectiveness of this change.