issue: add feature_request template [skip ci] (runatlantis#2397)

Signed-off-by: Rui Chen <rui@chenrui.dev>

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,43 @@
+---
+name: Feature request
+about: Propose a concrete new feature
+title: ''
+labels: 'feature'
+assignees: ''
+
+---
+
+<!--- Please keep this note for the community --->
+
+### Community Note
+
+* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request. Searching for pre-existing feature requests helps us consolidate datapoints for identical requirements into a single place, thank you!
+* Please do not leave "+1" or other comments that do not add relevant new information or questions, they generate extra noise for issue followers and do not help prioritize the request.
+* If you are interested in working on this issue or have submitted a pull request, please leave a comment.
+
+<!--- Thank you for keeping this note for the community --->
+
+---
+
+- [ ] I'd be willing to implement this feature ([contributing guide](https://github.com/runatlantis/atlantis/blob/master/CONTRIBUTING.md))
+
+**Describe the user story**
+
+A clear and concise description of what workflow is meant to be improved.
+Example: "As a developer, I often want to do <something>, but I often face <problem>".
+
+**Describe the solution you'd like**
+
+A clear and concise description of what you want to happen. Consider that atlantis is used
+by many people, and your particular use case might not make sense to implement in the core.
+
+**Describe the drawbacks of your solution**
+
+This section is important not only to identify future issues, but also for us to see whether
+you thought through your request. When filling it, ask yourself what are the problems we could
+have maintaining what you propose. How often will it break?
+
+**Describe alternatives you've considered**
+
+A clear and concise description of any alternative solutions or features you've considered,
+and why you think they wouldn't be good enough.