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

Start in renderer/renderer.go around lines 86-96 and trace how output-mode "group" processes multiversioned API types. Confirm the generated grouped documentation preserves every API version instead of leaving only the last version after repeated file writes.

Written by the indexing model from the issue text.