add feature request template (#692)

.github/ISSUE_TEMPLATE/dubbo-admin-feature-request-template.md

@@ -0,0 +1,20 @@
+---
+name: Dubbo-Admin feature request template
+about: If you would like to request a feature to Dubbo-Admin, please use this template.
+
+---
+
+- [ ] I have searched the [issues](https://github.com/apache/dubbo-admin/issues) of this repository and believe that this is not a duplicate.
+- [ ] I have checked the [REAMDE](https://github.com/apache/dubbo-admin/blob/develop/README.md) of this repository and believe that this is not a duplicate.
+
+### Is your feature request related to a problem? 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.