Add an issue template for Feature Requests (#1162)

## Summary
Currently we have issue templates for Bug Reports and for Plugin
Requests, but not for general Feature Requests. This PR adds a template
for the Feature Request case.

Author: loreto

.github/ISSUE_TEMPLATE/feature-request.md

@@ -0,0 +1,19 @@
+---
+name: Feature request
+about: Suggest an idea or new feature for this project
+title: '[Feature]: '
+labels: feature
+
+---
+
+**Is your feature request related to a problem you're trying to solve? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**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. Has the feature been requested before? If so, provide a link to the issue.