Rock update action should look at more than just `latest`

[Rock update action](https://github.com/canonical/observability/blob/main/.github/workflows/rock-update.yaml) is fetching the release that's marked as `latest`. However, sometimes, as a CVE response, upstream project might release more versions (example: [This Grafana CVE fix](https://grafana.com/blog/2024/08/14/grafana-security-release-medium-severity-security-fix-for-cve-2024-6837/?utm_source=grafana_news&utm_medium=rss) was released as [10.4.7](https://github.com/grafana/grafana/releases/tag/v10.4.7), [11.0.3](https://github.com/grafana/grafana/releases/tag/v11.0.3), [11.1.4](https://github.com/grafana/grafana/releases/tag/v11.1.4), but **none of them is marked as latest at the time of writing**).

We might need to fetch more than just `latest` release.

Start with .github/workflows/rock-update.yaml and trace how the Rock update action selects the upstream release. Use the Grafana CVE releases cited in the issue as examples; done means the action can find relevant releases beyond one marked latest.

Written by the indexing model from the issue text.