Add tool-specific RSS feeds

[ivelasq]

Could we add feeds for Quarto and Shiny to the RSS list, please?

cc: @cderv

[jeroenjanssens]

Yes we can. The cleanest solution would be to filter on the source field, just like how the legacy blogs are created (see https://opensource.posit.co/blog/q/). We can create an RSS feed for all of those for the same price. I don't think it makes sense to list them on the RSS overview page though.