Added an enhancement template for github (apache#7637)

### Motivation
Added a enhancement issue template for github so that its labelled correctly.

.github/ISSUE_TEMPLATE/enhancement_request.md

@@ -0,0 +1,20 @@
+---
+name: Enhancement request
+about: Suggest an enhancement for this project
+title: ''
+labels: type/enhancement
+assignees: ''
+
+---
+
+**Is your enhancement request related to a problem? Please describe.**
+A clear and concise description of what the enhancement is.
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.