Chore: Upgrade Go to 1.21.5 (#79329)
* bumping grafanas go version to 1.21.5
* adding how to upgrade go doc
* removing the whole ci-build and corresponding pipelines
* clarifying that we have to run make drone
* fixing starlark linter and removing unused code
* Adding note about enterprise
* trying to change the underyling image to avoid musl issues
* only need to golang one
(cherry picked from commit 4991e71b85)