Add milestone template

.github/ISSUE_TEMPLATE/milestone.yml

@@ -0,0 +1,51 @@
+name: Milestone
+
+# See the json schema to help you create / update this form
+# https://json.schemastore.org/github-issue-forms.json
+
+description: A concrete outcome that belongs to a bigger goal
+
+labels: ["Milestone"]
+
+body:
+  - type: textarea
+    attributes:
+      label: Context
+      description: Any context that helps understand the rationale for this milestone
+    validations:
+      required: false
+
+  - type: input
+    attributes:
+      label: Part of goal
+      description: "Milestone is part of this goal:"
+      placeholder: "put the issue number here"
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: Why
+      description: Motivation for the milestone
+      value: |
+        - 
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: Outcomes
+      description: High level things that need to be achieved
+      value: |
+        - [ ] 
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: What
+      description: Concrete tasks needed to achieve the desired outcomes. Will become Epics.
+      value: |
+        - [ ] 
+    validations:
+      required: true