[mongodb-core] add support for any operation name and add missing query tag

[rochdev]

This PR improves the MongoDB integration by adding support for any operation name and by adding the mongodb.query tag to make the query available in the UI. The previous version used a static list of operation name. Now we instead use the first key of the command object, which is the same behavior as the built-in APM events in new versions of the mongodb-core module.

Fixes #260

[brettlangdon]

for sanitize, what does it do with arrays?

it seems like:

{
  $or: [ {}, {} ]
}

would become

{
  $or: ?
}

❓

[brettlangdon]

🔥 🔥 🔥

[brettlangdon]

This is what we do in dd-trace-py: https://github.com/DataDog/dd-trace-py/blob/7db12f1c398c07cd5baf91c571aed672dbb6496d/ddtrace/contrib/pymongo/client.py#L207-L232

[rochdev]

for sanitize, what does it do with arrays?

Right now it's stored as a single ?. The idea was that since every field can potentially be an array, and each array can be of variable size, this could lead to a lot of different resources.

@brettlangdon This behavior is the current behavior which this PR doesn't alter, so I would prefer to discuss this in another issue instead as it would introduce a breaking change to the resource name.

[brettlangdon]

@brettlangdon This behavior is the current behavior which this PR doesn't alter, so I would prefer to discuss this in another issue instead as it would introduce a breaking change to the resource name.

👍

[brettlangdon]

lgtm