API sets tracecontext, baggage as default global propagators

[pellared]

opentelemetry-python/opentelemetry-api/src/opentelemetry/propagate/__init__.py

Lines 124 to 146 in ec3053e

	propagators = []
	# Single use variable here to hack black and make lint pass
	environ_propagators = environ.get(
	OTEL_PROPAGATORS,
	"tracecontext,baggage",
	)
	for propagator in environ_propagators.split(","):
	propagator = propagator.strip()
	try:
	propagators.append( # type: ignore
	next( # type: ignore
	iter_entry_points("opentelemetry_propagator", propagator)
	).load()()
	)
	except Exception: # pylint: disable=broad-except
	logger.exception(
	"Failed to load configured propagator `%s`", propagator
	)
	raise
	_HTTP_TEXT_FORMAT = composite.CompositePropagator(propagators) # type: ignore

This behavior is in direct conflict with the API specification:

The OpenTelemetry API MUST use no-op propagators unless explicitly configured otherwise.

I think the SDK could do that, but not the API.

Side note: I find such logic in init violating the style guide: https://google.github.io/styleguide/pyguide.html#25-global-variables

Origin: Found by @Aneurysm9 when discussing open-telemetry/opentelemetry-go#2611