ext/pymongo: Add instrumentor

[mauriciovasquezbernal]

This PR implements the Instrumentor interface for the Pymongo integration. It also implements a way to disable instrumentation.

I compared with the DataDog donated implementation available at https://github.com/open-telemetry/opentelemetry-python-contrib/tree/master/reference/ddtrace/contrib/pymongo, the already existing implementation is good enough and we do not need to take any from that in this case.

I'm opening a new PR to supersedes #598 to avoid reviewing and approving my own changes there.

How to try:

# install
pip install -e ext/opentelemetry-ext-pymymongo/
# set up test db
opentelemetry-ext-docker-tests/tests
docker-compose up

pymongo_example.py:

# Configuration code
from opentelemetry import trace

from opentelemetry.sdk.trace.export import (
    SimpleExportSpanProcessor,
    ConsoleSpanExporter,
)

trace.get_tracer_provider().add_span_processor(
    SimpleExportSpanProcessor(ConsoleSpanExporter())
)

# Real example starts here
import os

from pymongo import MongoClient

MONGODB_HOST = os.getenv("MONGODB_HOST ", "localhost")
MONGODB_PORT = int(os.getenv("MONGODB_PORT ", "27017"))
MONGODB_DB_NAME = os.getenv("MONGODB_DB_NAME ", "opentelemetry-tests")
MONGODB_COLLECTION_NAME = "test"

client = MongoClient(
    MONGODB_HOST, MONGODB_PORT, serverSelectionTimeoutMS=2000
)
db = client[MONGODB_DB_NAME]
collection = db[MONGODB_COLLECTION_NAME]

collection.insert_one({"name": "testName", "value": "testValue"})

OPENTELEMETRY_PYTHON_TRACER_PROVIDER=sdk_tracer_provider opentelemetry-auto-instrumentation pymongo_example.py

If everything went fine you see some spans on the terminal.

[hectorhdzg]

LGTM only added some small suggestions

[toumorokoshi]

LGTM! Thanks.

[toumorokoshi]

I notice this snippet is almost identical to the above code. Don't know if it's worth refactoring into a utility method though.

[mauriciovasquezbernal]

Do you mean the following snippet?

        if not self.is_enabled:
            return

?

[toumorokoshi]

nvm. I maybe be going crazy, but I thought a diff verifying significantly more standard attributes like db type.