test(harness): add end-to-end harness test for --telemetry flag

Verifies that enabling OpenTelemetry tracing via --telemetry does not affect
the served response: the server span wraps the request handler transparently
and the mock response is returned as normal.

Refs #2804

Author: Ignacio-Vidal

test-harness/specs/telemetry/telemetry-enabled-serves-response.txt

@@ -0,0 +1,23 @@
+====test====
+When prism is started with the --telemetry flag, OpenTelemetry tracing is enabled but
+responses are still served normally (the server span wraps the handler transparently).
+====spec====
+openapi: 3.0.2
+paths:
+  /todos:
+    get:
+      responses:
+        200:
+          description: Get Todo Items
+          content:
+            'application/json':
+              example: hello
+====server====
+mock -p 4010 --telemetry ${document}
+====command====
+curl -i -X GET http://localhost:4010/todos -H "accept: application/json"
+====expect-loose====
+HTTP/1.1 200 OK
+content-type: application/json
+
+"hello"