Simplify Release Notes section of the PR checklist
Simplify Release Notes section of the PR checklist

This commit simplifies the release notes section by replacing the existing
comment with a default `NONE` release note. In addition it updates the
submitter checklist instruction to expect the submitter to update the release
note if needed. In addition, it adds two new items to the checklist - 1. to add
a kind label using the /kind command and 2. add an `action required:` to the
release note if needed.

Fixes #5093

Signed-off-by: Dibyo Mukherjee <7d445be0c0af41c00c371a1f7b3669c3331901f5@google.com>

tektoncd/pipeline,tektoncd/pipeline