RedisInstrumentor doesn't respect "supress_instrumentation" flag

[martimors]

We have a healtcheck in our app, which checks Redis connectivity using the PING command. It is very uninteresting to trace, and spams our trace storage so much that we cannot currently use the RedisInstrumentor for our application.

Other instrumentor libraries, such as the requests one and the gRPC one, check for this flag when deciding whether or not to start a new trace. The same solution could be applied here.

Same issue in gRPC client instrumentor: #559
Nice illustration of the exact way to fix it for the Redis instrumentor:

opentelemetry-python-contrib/instrumentation/opentelemetry-instrumentation-requests/src/opentelemetry/instrumentation/requests/__init__.py

Lines 129 to 131 in b6d77f1

	if context.get_value(
	_SUPPRESS_INSTRUMENTATION_KEY
	) or context.get_value(_SUPPRESS_HTTP_INSTRUMENTATION_KEY):

(this is how I fixed it for the Redis instrumentor too).

I've already implemented and verified a fix for this, just waiting for internal approval to submit it.

Steps to reproduce

from opentelemetry.instrumentation.redis import RedisInstrumentor
from redis import Redis
from opentelemetry.context import attach, detach, set_value
from opentelemetry.instrumentation.utils import _SUPPRESS_INSTRUMENTATION_KEY

RedisInstrumentor.instrument()

client = Redis()
token = attach(set_value(_SUPPRESS_INSTRUMENTATION_KEY, True))
client.ping()
detach(token)

What is the expected behavior?
No trace

What is the actual behavior?
Trace

Additional context
Add any other context about the problem here.