feat: PR template

Author: typotter

.github/pull_request_template.md

@@ -0,0 +1,23 @@
+---
+labels: mergeable
+---
+_Eppo Internal_
+[//]: #  (Link to the issue or doc corresponding to this chunk of work)
+🎟️ Fixes: #__issue__
+📜 Design Doc (if applicable)
+
+## Motivation and Context
+[//]: #  (Why is this change required? What problem does it solve?)
+
+## Description
+[//]: # (Describe your changes in detail)
+
+## How has this been documented?
+[//]: # (Please describe how you documented the developer impact of your changes; link to PRs or issues)
+
+## How has this been tested?
+[//]: # (Please describe in detail how you tested your changes)
+
+
+[//]: # (OPTIONAL)
+[//]: # (Add one or multiple labels: enhancement, refactoring, bugfix)