feature_proposal.md: add initial feature proposal template

.github/ISSUE_TEMPLATE/feature-proposal.md

@@ -0,0 +1,46 @@
+---
+name: Feature proposal
+about: Suggest a way to make improve this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!--
+
+Hey! Thanks for opening an issue!
+
+We really recommend you including screenshots and logs to help us to achieve a shared understanding of the issue.
+
+-->
+
+**What is the problem that you wish to solve?**
+
+> Please provide a clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**What is the best solution to solve the above problem?**
+
+> Please provide a clear and concise description of what the solution is.
+
+**What are the alternative solutions that you have considered?**
+
+> Please provide a clear and concise description of any alternative solutions or features you've considered.
+
+**How will this project improvement be tested?**
+
+> Please include your thoughts on how we can ensure that this improvement is tested thoroughly.
+
+**In what environment do you hope to see this improvement?**
+- Pinniped server version:
+- Pinniped client version:
+- Pinniped container image (if using a public container image):
+- Pinniped configuration (what IDP(s) are you using? what downstream credential minting mechanisms are you using?):
+- Kubernetes version (use `kubectl version`):
+- Kubernetes installer & version (e.g., `kubeadm version`:
+- Cloud provider or hardware configuration:
+- OS (e.g: `cat /etc/os-release`):
+- Kernel (e.g. `uname -a`):
+- Others:
+
+**What else do we need to know?**