Docs generated in output-mode "group" are missing versions for multiversioned APIs

For a multi versioned API type, when generating a output-mode "group" rendering, the generated one only contains 1 version of the api.
This is primarily becasue we are overwiting the same named file for all the versions one at a time, thus the last one is what is left generated

primarily due to the following code block we iterate over all the gvd without first grouping them based on the group. https://github.com/elastic/crd-ref-docs/blob/7de989285647936ac62ea1ff8887e25e0056bc58/renderer/renderer.go#L86-L96