Add issue template for release checklist.

Author: mbjones

.github/ISSUE_TEMPLATE/release_checklist.md

@@ -0,0 +1,32 @@
+---
+name: Release Checklist
+about: A release-prep checklist
+title: "Release Checklist for x.y.z"
+labels:
+  - release
+assignees: []
+hidden: true    # do NOT show in template picker every time someone creates a new issue
+---
+
+## Release checklist
+
+- [ ] Create a branch named `task-<issueNum>-release-<releaseVer>-prep`, and do the following:
+  - [ ] **pom.xml**: Update `<version>x.y.z</version>`
+  - [ ] Grep codebase for previous release number, just in case
+  - [ ] **RELEASE-NOTES.md**:
+    - [ ] Update for new app
+    - [ ] DON'T FORGET TO SET CORRECT RELEASE DATE!
+  - [ ] PR & merge release prep branch to `develop`
+- [ ] PR & merge `develop` -> `main`
+- [ ] Merge `main` back to `develop`
+  ```shell
+  git checkout develop; git merge main --ff-only
+  git push
+  ```
+- [ ] Tag the release; look up the `<commit-sha>` from `git log`, then:
+  ```shell
+  # Always use annotated tags (-a) for releases
+  git tag -a x.y.z <commit-sha> -m "d1_common_java Release x.y.z"
+  git push --tags    ## IMPORTANT - DON'T FORGET THIS!
+  ```
+- [ ] Add to GH `Releases` page