Add template for code maintenance task (#10251)

We need this to create issues to track work like "update venv.py to
address upcoming pip build system deprecation" since we no longer have a
blank issue template.

.github/ISSUE_TEMPLATE/task.yaml

@@ -0,0 +1,15 @@
+name: Task
+description: A codebase upkeep task such as managing deprecations and refactoring
+title: "[Task]: "
+type: Task
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Task description
+      description: Describe the work that needs to happen, and why.
+      placeholder: >
+        For example, "In issue [link here], we noted that we cannot update [dependency] until
+        [something happens]. That thing has happened, so now we should update [dependency]."
+    validations:
+      required: true