feat: opt-in enablement of the instrumentation telemetry client (#386)

* feat: opt-in enablement of the instrumentation telemetry client

* Update datadog_lambda/tracing.py

Co-authored-by: Alberto Vara <a.vara.1986@gmail.com>

* Fix linter

---------

Co-authored-by: Alberto Vara <a.vara.1986@gmail.com>

Author: Julio-Guerra

datadog_lambda/tracing.py

@@ -55,6 +55,15 @@
 
 dd_trace_context = {}
 dd_tracing_enabled = os.environ.get("DD_TRACE_ENABLED", "false").lower() == "true"
+if dd_tracing_enabled:
+    # Enable the telemetry client if the user has opted in
+    if (
+        os.environ.get("DD_INSTRUMENTATION_TELEMETRY_ENABLED", "false").lower()
+        == "true"
+    ):
+        from ddtrace.internal.telemetry import telemetry_writer
+
+        telemetry_writer.enable()
 
 propagator = HTTPPropagator()