[statsd] Always terminate packets with newline

[sgnn7]

What does this PR do?

Adds newline (\n) to all packets sent to the DogStatsd endpoint

Description of the Change

To prevent processing of packets that are incomplete by the time they
reach the server for whatever reason, we now add a newline to end of
all of our packets so that the server can recognize and discard partial
messages/metrics.

Alternate Designs

Possible Drawbacks

One character additionally sent with each packet (minimal impact on buffered clients)

Verification Process

• Run the test suite (python3 -m unittest -vvv tests.unit.dogstatsd.test_statsd.TestDogStatsd)

Alternatively:

• Start a fake statsd server on a separate terminal (./tests/util/fake_statsd_server.py UDP)
• Send a metric and ensure it has a newline at the end on the server's received packet output:

$ python3
>>> from datadog import initialize,statsd
>>> initialize(statsd_host="localhost", statsd_port=<port_from_server>)
>>> statsd.increment("home.page.hits")

Additional Notes

Release Notes

N/A

Review checklist (to be filled by reviewers)

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

[sgnn7]

/azp run

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[gh123man]

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