chore: Move tracing decorators into the codebase (#4623)

* Vendorize tracing, finally fix service name issues

* Upgrade datadaog-metrics, rename decorators -> tracing

* lint

server/env.ts

@@ -343,6 +343,11 @@ export class Environment {
    */
   public DD_API_KEY = process.env.DD_API_KEY;
 
+  /**
+   * The name of the service to use in DataDog.
+   */
+  public DD_SERVICE = process.env.DD_SERVICE ?? "outline";
+
   /**
    * Google OAuth2 client credentials. To enable authentication with Google.
    */