[FEAT]: Add support for Public Keys API (#2945)

* Add support for /mets/public_keys/<keyType>

* "files.insertFinalNewline": false

* revert and make setttings.json change csharp only

* formatting

* remove final new line

---------

Co-authored-by: Nick Floyd <139819+nickfloyd@users.noreply.github.com>

Octokit.Reactive/Clients/IObservableMetaClient.cs

@@ -10,6 +10,11 @@ namespace Octokit.Reactive
     /// </remarks>
     public interface IObservableMetaClient
     {
+        /// <summary>
+        /// Returns a client to get public keys for validating request signatures.
+        /// </summary>
+        IObservablePublicKeysClient PublicKeys { get; }
+
         /// <summary>
         /// Retrieves information about GitHub.com, the service or a GitHub Enterprise installation.
         /// </summary>