Creating a PR template (#1546)

.github/pull_request_template.md

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+## ✅ What
+ 
+<!-- A brief description of the changes in this PR. -->
+ 
+## 🤔 Why
+ 
+<!-- A brief description of the reason for these changes. -->
+ 
+## 👩‍🔬 How to validate if applicable
+ 
+<!-- Step-by-step instructions for how reviewers can verify these changes work as expected. -->
+ 
+## 🔖 Related links
+ 
+- [Issues](<link>)
+- [Team thread](<link>)
+- [Documents](<link>)
+- [Email Subject]