Allow easier adding of versions

[hasufell]

Input:

1. base url like https://downloads.haskell.org/~ghc/9.0.1
2. SHA256SUM file
3. metadata file (e.g. ghcup-0.0.6.yaml)
4. changelog URL

Output:

• updated YAML

---

Things to consider:

1. getting the yaml anchors right
2. getting viPostRemove, viPostInstall etc right
3. not missing the source tarball
4. getting the tags right (some tags are unique (e.g. recommended and latest), some are not (e.g. old))
5. getting the subdirectories right