Updates PR template for screenshots and test instructions (#4042)

Signed-off-by: Ashwin P Chandran <ashwinpc@amazon.com>

Author: ashwin-pc

.github/pull_request_template.md

@@ -4,8 +4,20 @@
 
 ### Issues Resolved
 
-<!-- List any issues this PR will resolve. -->
-<!-- Example: closes #1234 -->
+<!-- List any issues this PR will resolve. Prefix the issue with the keyword closes, fixes, fix -->
+<!-- Example: closes #1234 or fixes <Issue_URL> -->
+
+## Screenshot
+
+<!-- Attach any relevant screenshots. Any change to the UI requires an attached screenshot in the PR Description -->
+
+## Testing the changes
+
+<!--
+  Please provide detailed steps for validating your changes. This could involve specific commands to run,
+  pages to visit, scenarios to try or any other information that would help reviewers verify
+  the functionality of your change
+-->
 
 ### Check List