Add sitemap configuration to configuration file

[darklinkpower]

Just a small update. I just tried searching on google for something in the manual and for some reason it's linking to the old locations:

From a quick search I stumbled upon this and the reason could be that the docs lack a sitemap.

This PR helps to generate the sitemap while building the site, I don't know if it will fix the issue of Google not picking it up but it won't hurt and I think it's good practice to have one.

---

Example of generate sitemap.xml file:

<?xml version="1.0" encoding="utf-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://api.playnite.link/docs/api/index.html</loc>
    <lastmod>2023-10-09T05:52:39-06:00</lastmod>
    <changefreq>daily</changefreq>
    <priority>0.5</priority>
  </url>
  <url>
    <loc>https://api.playnite.link/docs/changelog.html</loc>
    <lastmod>2023-10-09T05:52:39-06:00</lastmod>
    <changefreq>daily</changefreq>
    <priority>0.5</priority>
  </url>
   ...

[JosefNemec]

It's because Google is really slow re-indexing. Not sure if sitemap will help much. Manual wasn't indexed at all even couple weeks ago, I had to explicitly request the site to be indexed (Bing for example had no issue doing it automatically).

[darklinkpower]

I see, fingers crossed this helps by some luck.

[darklinkpower]

Good news, this seems to have fixed the docs not being indexed by Google. I'm surprised by how fast this was fixed.