Fix RSS feeds for blog and reports pages

[sarathms]

This was reported in the IRC channel by pabs:

• [ ] The RSS feeds for the blog listing page and the research reports page are generated with no relevant content from their HTML pages. Before these pages were carved out from https://ooni.org/post/, the RSS feed for the page worked as expected. It still does.

• [ ] We can use the attribute rel="alternate" instead of rel="feed" to comply with RSS autodiscovery. Although it seems to work fine in most cases as-is.

• [ ] The .RSSLink variable in Hugo now throws a deprecation notice and we need to switch to the recommended alternative.

Building sites … WARN 2020/09/28 18:56:24 Page's .RSSLink is deprecated and will be removed in a future release. Use the Output Format's link, e.g. something like: 
    {{ with .OutputFormats.Get "RSS" }}{{ .RelPermalink }}{{ end }}.
WARN 2020/09/28 18:56:24 Page's .URL is deprecated and will be removed in a future release. Use .Permalink or .RelPermalink. If what you want is the front matter URL value, use .Params.url.

[pabs3]

FTR, rel="feed" is the newer HTML5 standard that broke compatibility with the older RSS autodiscovery standard rel="alternate" for no particular reason, probably the folks who wrote the newer standard didn't know about the older standard. Consequently some RSS clients support the older standard but don't support the newer standard and vice-versa. Based on my research I thought only Firefox knows about the newer standard but it sounds like there might be more based on your link above. So I would suggest using both standards for maximum compatibility.

[bassosimone]

@sarathms assigned this to you. Please reassign to some other team member if needed.

[hellais]

It was reported that this is still an issue. We should look into this and ensure only the /post/index rss feeds are shared via meta tags