Add template for "release" issues (#6740)

As we prepare to do a release, we generally create an issue that
contains instructions and checklists for the mechanics of the release.
This change adds a template for these issues.

Author: damyanp

.github/ISSUE_TEMPLATE/release.md

@@ -0,0 +1,57 @@
+---
+name: Release
+about: Create a tracking issue for a release
+title: 'Release 1.x.xxxx'
+labels: []
+assignees: ''
+
+---
+
+# Schedule
+
+- [ ] MM/DD/YYYY - Release branch forks from `main`
+    - At this point, changes must be cherry-picked into the release branch in
+      order for them to be included in the release.
+- [ ] MM/DD/YYYY - Release Candidate 1 (begin Ask Mode[^1] for release branch).
+    - At this point, changes must be approved by @microsoft/hlsl-release
+- [ ] MM/DD/YYYY - Final Release Candidate
+- [ ] MM/DD/YYYY - Target Release Date
+
+
+# Tasks
+
+## Before Fork
+
+This part of the release process is to 'prime the pump' - that is to make sure
+that all the various parts of the engineering system are set into place so that
+we are confident we can generate builds for the new branch
+
+- [ ] Update version number
+- [ ] Create the release branch from `main`
+    - The release branch is kept into sync with main via regular fast-forward
+      merges.
+- [ ] Internal branches and build pipelines configured
+    - Verify that the engineering system can build:
+    - [ ] Zip files for github release
+    - [ ] NuGet package
+    - [ ] VPack
+- [ ] Final merge of `main` into the release branch
+
+## After Fork
+
+- [ ] Update README.md
+- [ ] Create draft of Release post on GitHub
+
+## Quality Sign Off
+
+- [ ] Microsoft Testing Sign-off (@pow2clk)
+- [ ] Google Testing Sign-off (@s-perron / @Keenuts)
+
+## Release
+
+- [ ] Tag final release and post binaries
+
+
+[^1]: [Ask Mode](https://devblogs.microsoft.com/oldnewthing/20140722-00/?p=433)
+    is a Microsoft-ism to denote when changes require approval before accepting
+    merges. For DXC this will require approval from @microsoft/hlsl-release