feat: Initialize Zastava Webhook service with TLS and Authority authentication

- Added Program.cs to set up the web application with Serilog for logging, health check endpoints, and a placeholder admission endpoint.
- Configured Kestrel server to use TLS 1.3 and handle client certificates appropriately.
- Created StellaOps.Zastava.Webhook.csproj with necessary dependencies including Serilog and Polly.
- Documented tasks in TASKS.md for the Zastava Webhook project, outlining current work and exit criteria for each task.

src/StellaOps.Authority/StellaOps.Authority.Plugins.Abstractions/AuthorityClientMetadataKeys.cs

@@ -9,4 +9,5 @@ public static class AuthorityClientMetadataKeys
     public const string AllowedScopes = "allowedScopes";
     public const string RedirectUris = "redirectUris";
     public const string PostLogoutRedirectUris = "postLogoutRedirectUris";
+    public const string SenderConstraint = "senderConstraint";
 }