chore: add epic template

.github/ISSUE_TEMPLATE/epic.md

@@ -0,0 +1,22 @@
+---
+name: Epic
+about: An epic is a collection of user stories. It can be used to gather features sharing the same goal (e.g. User login management, Migration, Purchase etc.). 
+title: Epic
+labels: Epic
+assignees: ''
+
+---
+
+**Why do you want to add this epic ?**
+Explain how this is a solution for ARA, what value(s) does it add (e.g. "ARA access does not require any login, anyone can do anything and that can be a problem (for instance, project deletion)").
+
+**Description**
+What is the epic about ? Feel free to detail as many as you can.
+
+**Features**
+- feature 1 (#xx)
+- feature 2 (#yy)
+- ...
+
+**Additional context**
+Add any other context or screenshots about the epic request here or even mockups of screen modifications if you have made any :)