chore: add pull request template

.github/pull_request_template.md

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+**Screenshots**
+
+**Related Issue**
+E.g: *Closes/Fixes #1234*
+
+- [ ]  **Functionality validation**
+    - [ ]  Feature working as described in the related issue
+    - [ ]  New environmental variables have been set
+    - [ ]  New API services methods have tests
+    - [ ]  Code errors are being logged in the code health service
+- [ ]  **Product validation**
+    - [ ]  UI changes look the same as in Figma
+    - [ ]  Usage events are being sent to the product analytics service
+    - [ ]  New common components have been documented in Storybook
+    - [ ]  Preview link if it’s a customer facing issue
+- [ ] **Documentation**
+    - [ ] README updated
+    - [ ] New API changes are documented
+- [ ] **Accessibility**
+    - [ ] UI changes are accessible