Add client side aggregation

[andrewqian2001datadog]

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What does this PR do?

Project description This PR adds simple client side aggregation (aggregating metrics before they are received by the agent) for the python client. This PR combines two previous PRs together (1, 2)

Client side aggregation has already been implemented in Go, Java, and the C# dogstatsd clients

Description of the Change

Periodically aggregates metrics (Count, Gauge, Set) for a given statsd_aggregation_flush_interval and then sends the aggregated metrics to intake. A metric will be aggregated if statsd_disable_aggregating is False and there was another matching context sent within the same flush interval.

Verification Process

Unit tests that verify the aggregator.py class matches the existing behavior in the client side aggregator for the go client.

Unit tests that verify the new metric objects (merics.py) match the existing behavior in the client side aggregator for Go.

Local testing: Confluence doc More Docs

Bench Mark tests (TODO as a stretch goal)

Additional Notes

We currently do not allow buffering and aggregation at the same time, if both enabled, aggregation will occur instead of buffering.

Release Notes

Review checklist (to be filled by reviewers)

• [x] Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [x] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [x] PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• [x] PR should not have do-not-merge/ label attached.
• [ ] If Applicable, issue must have kind/ and severity/ labels attached at least.

[andrewqian2001datadog]

/merge

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