add support for retrospective

[UlisesGascon]

Main changes

This PR will include the Top threads of the week/month for the Node.js org in Github by including a link to the last report available in https://github.com/cutenode/retro-weekly (cc: @bnb @wesleytodd)

How it works

• 1. Checks the config file to get the reference for report (date)
• 2. Try to reach the URL and get the Markdown in raw format like https://raw.githubusercontent.com/cutenode/retro-weekly/main/retros/2023-10-22.md
• 3. Extract the relevant data (title, description, fromDate y toDate) using basic string manipulation.
• 4. Generate a valid feed item like:

  <item>
    <title>Retrospective for nodejs from 2023-10-22 to 2023-10-29</title>
    <description><![CDATA[<p>Reporting on 35 Issues from 29 authors, 65 Pull Requests from 33 authors, and 9 Discussions from 7 authors.</p>]]></description>
    <pubDate>Sun, 22 Oct 2023 02:00:00 BST</pubDate>
    <link>https://github.com/cutenode/retro-weekly/blob/main/retros/2023-10-22.md</link>
    <guid>https://github.com/cutenode/retro-weekly/blob/main/retros/2023-10-22.md</guid>
  </item>

• 5. Add the new item in the feed
• 6. Save the new dates in the config

Context

• Close Idea: Top threads of the week/month #42
• Related Social / sharing news next-10#231 (comment)

[mhdawson]

LGTM