Convert each registry-entry from .md to .yml and move into data folder

[chalin]

• Closes Registry cleanup: make entry files pure data files #2247
• Converts registry-entry .md files to .yml, since each entry file only had YAML front matter.
• Moves the registry-entry files into the repo's data folder under a registry directory.
• This change ensures that the individual registry entries no longer show up in the sitemap.xml file.
• No content changes were made to the

If y'all agree with this change, I'll update the other registry-entry related assets in a followup PR.

Preview: https://deploy-preview-2249--opentelemetry.netlify.app/registry

---

If you hover over Search, you'll now see how many entries there are:

Other than that, the search form functions as it did before.

Regarding the sitemap.xml cleanup:

$ (cd public && git diff sitemap.xml) | head -20 
diff --git a/sitemap.xml b/sitemap.xml
index dc048eb83..abf04933e 100644
--- a/sitemap.xml
+++ b/sitemap.xml
@@ -510,1795 +510,205 @@
     <loc>https://opentelemetry.io/blog/2019/opentelemetry-governance-committee-explained/</loc>
     <lastmod>2022-09-15T20:56:31+02:00</lastmod>
   </url><url>
-    <loc>https://opentelemetry.io/registry/otel-dotnet/</loc>
-    <lastmod>2020-10-16T13:04:06-04:00</lastmod>
-  </url><url>
-    <loc>https://opentelemetry.io/registry/instrumentation-dotnet-runtime/</loc>
-    <lastmod>2022-08-16T12:49:13-07:00</lastmod>
-  </url><url>
-    <loc>https://opentelemetry.io/docs/reference/specification/schemas/file_format_v1.0.0/</loc>
-  </url><url>
-    <loc>https://opentelemetry.io/docs/reference/specification/schemas/file_format_v1.1.0/</loc>
-  </url><url>
-    <loc>https://opentelemetry.io/registry/instrumentation-ruby-action-pack/</loc>
-    <lastmod>2022-10-11T07:54:22-06:00</lastmod>