[release process] add release template (open-telemetry#4955)

This new template can be used when creating a new release.

Fixes open-telemetry#4883

.github/ISSUE_TEMPLATE/release.md

@@ -0,0 +1,18 @@
+---
+name: Release
+about: Create an issue for releasing new versions
+title: 'Release vX.X.X'
+labels: release
+assignees: ''
+
+---
+
+Like #4522, but for vX.X.X
+
+- [ ] Prepare core release vX.X.X
+- [ ] Tag and release core vX.X.X
+- [ ] Prepare contrib release vX.X.X
+- [ ] Tag and release contrib vX.X.X
+- [ ] Prepare otelcol-releases vX.X.X
+- [ ] Release binaries and container images vX.X.X
+- [ ] Release the operator vX.X.X