feat(tooling): add rc bump for release candidates (0.39.0-rc.2 -> 0.39.0-rc.3) (weaveworks#5313)

Author: casibbald

.github/release-notes-template.md

@@ -0,0 +1,18 @@
+# Release v{{VERSION}}
+
+## Summary
+[2-3 sentence overview of this release]
+
+## Changes
+
+### Features
+- [List enhancements and new features from commits]
+
+### Fixes
+- [List bug fixes from commits]
+
+### Other
+- [Docs, chore, refactor, build, ci, etc.]
+
+---
+*Generated from commits since the previous release.*