Allow django to be instrumented automatically

Django instrumentation required that OTEL_PYTHON_DJANGO_INSTRUMENT
environment variable be set to "True" by users. All other
instrumentations are enabled out of the box and there is no apparent
reason to disable Django by default. This commit changes the logic so
that Django instrumentation is applied by default. Users can set
`OTEL_PYTHON_DJANGO_INSTRUMENT` env var to `"False"` to disable it.

docs/examples/django/README.rst

@@ -36,7 +36,6 @@ Execution of the Django app
 
 Set these environment variables first:
 
-#. ``export OTEL_PYTHON_DJANGO_INSTRUMENT=True``
 #. ``export DJANGO_SETTINGS_MODULE=instrumentation_example.settings``
 
 The way to achieve OpenTelemetry instrumentation for your Django app is to use
@@ -100,6 +99,13 @@ output similar to this one:
 The last output shows spans automatically generated by the OpenTelemetry Django
 Instrumentation package.
 
+Disabling Django Instrumentation
+--------------------------------
+
+Django's instrumentation can be disabled by setting the following environment variable.
+
+#. ``export OTEL_PYTHON_DJANGO_INSTRUMENT=False``
+
 References
 ----------
 

instrumentation/opentelemetry-instrumentation-django/src/opentelemetry/instrumentation/django/__init__.py

@@ -41,7 +41,7 @@ def _instrument(self, **kwargs):
         # built inside the Configuration class itself with the magic method
         # __bool__
 
-        if not Configuration().DJANGO_INSTRUMENT:
+        if Configuration().DJANGO_INSTRUMENT is False:
             return
 
         # This can not be solved, but is an inherent problem of this approach: