Create the RSS 2.0 feed

[amieiro]

This PR adds:

• A new class to generate an RSS 2.0 feed.
• Two routes (/events/feed and /events/rss) to get the RSS feed.
• A new method (get_current_and_upcoming_events) in the event repository to get all events that are currently active or happening in the future, in order by the start date.

The:

• The pubDate element defines the last publication date for an item.
  • In the main file, the pubDate is the date of the last update of all events in the RSS file.
  • In the event (item), the pubDate is the last update of this event.
• The lastBuildDate element defines the last-modified date of the content of the feed, so it is the same value that the pubDate in the main file.

I have used the http://purl.org/rss/1.0/modules/event/ namespace to be able to add the ev:startdate and ev:enddate elements to each event.

Date format:

• The pubDate has the DATE_RSS format: 'D, d M Y H:i:s O'.
• the ev:startdate and ev:enddate have the DateTimeInterface::ATOM format: 'Y-m-d\TH:i:sP'.

You can validate the RSS feed using the W3C Feed Validation Service, coping and pasting the generated content. You will get some warning like this, because the local URL is not accessible from this tool:

One example with the generated RSS feed:

<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:atom="http://www.w3.org/2005/Atom" xmlns:ev="http://purl.org/rss/1.0/modules/event/" version="2.0">
   <channel>
      <title>WordPress.org Global Translation Events</title>
      <link>https://glotpress.test/glotpress/events/</link>
      <description>WordPress.org Global Translation Events</description>
      <language>en-us</language>
      <pubDate>Sat, 29 Jun 2024 10:13:45 +0000</pubDate>
      <lastBuildDate>Sat, 29 Jun 2024 10:13:45 +0000</lastBuildDate>
      <docs>https://www.rssboard.org/rss-specification</docs>
      <generator>Translation Events</generator>
      <atom:link href="https://glotpress.test/glotpress/events/rss/" rel="self" type="application/rss+xml" />
      <item>
         <title>July event</title>
         <link>https://glotpress.test/glotpress/events/july-event__trashed/</link>
         <description>Lorem ipsum</description>
         <enclosure url="https://glotpress.test/glotpress/events/image/366/" type="image/png" length="1200" />
         <pubDate>Wed, 10 Apr 2024 23:26:18 +0000</pubDate>
         <ev:startdate>2024-07-01T12:01:00+00:00</ev:startdate>
         <ev:enddate>2024-08-01T11:59:00+00:00</ev:enddate>
         <guid>https://glotpress.test/glotpress/events/july-event__trashed/</guid>
      </item>
      <item>
         <title>August event</title>
         <link>https://glotpress.test/glotpress/events/august-event__trashed/</link>
         <description />
         <enclosure url="https://glotpress.test/glotpress/events/image/365/" type="image/png" length="1200" />
         <pubDate>Thu, 21 Mar 2024 12:17:19 +0000</pubDate>
         <ev:startdate>2024-07-31T22:00:00+00:00</ev:startdate>
         <ev:enddate>2024-08-31T01:09:09+00:00</ev:enddate>
         <guid>https://glotpress.test/glotpress/events/august-event__trashed/</guid>
      </item>
      <item>
         <title>September event</title>
         <link>https://glotpress.test/glotpress/events/september-event/</link>
         <description>Lorem ipsum</description>
         <enclosure url="https://glotpress.test/glotpress/events/image/532/" type="image/png" length="1200" />
         <pubDate>Thu, 09 May 2024 10:15:59 +0000</pubDate>
         <ev:startdate>2024-08-31T22:01:00+00:00</ev:startdate>
         <ev:enddate>2024-09-30T21:59:00+00:00</ev:enddate>
         <guid>https://glotpress.test/glotpress/events/september-event/</guid>
      </item>
   </channel>
</rss>

Fixes #217.

[psrpinto]

Looks great!

[akirk]

Could we add a <link rel="alternate" href=""> to expose this?