CI: Support more version formats in publishing (#94575)
* cleanup dead code
* add tests and rewrite publish grafanacom steps to reuse
* add pkg/build tests; don't upload CDN assets on grafana releases
(cherry picked from commit 7a2edd35d5)
* Move and rename genversions.go and tests
* Fix lint - bring back cli.Exit
* Move package.json and fix tests
* Add necessary env vars for promote event