RFE: Add supported Ansible versions to the collection "index.html"

[tremble]

See for example: https://ansible-collections.github.io/amazon.aws/branch/main/collections/amazon/aws/index.html

Since teams are now starting to build the docs independently, and module consumers are installing collections that don't match the big-tent "Ansible" version they have installed it would be good if the index page lists which versions of Ansible are supported.

I think this is generated from src/antsibull_docs/data/docsite/plugins_by_collection.rst.j2 but I don't know if/how this can be pulled from meta/runtime.yml

[felixfontein]

That part of meta/runtime.yml isn't loaded right now, but that should be doable. I will probably take a look at it soon.

[felixfontein]

A first implementation is in #49.

[tremble]

49 has merged, I think we can close this RFE off. Thanks @felixfontein