#2079 SMS Content Length StatsD Metric

[mchlwellman]

Description

This PR adds a new metric type to the StatsD client, histogram, which matches the metric that Datadog has added. This metric type is used to track sms content length. In Datadog, normal statsd gauges are flushed every 10 seconds, and only the last value is retained, making it unsuitable for tracking sms content length.

issue #2079

How Has This Been Tested?

This was deployed and tested in dev, and perf by deploying and observing the metrics in Datadog.

Checklist

• [x] I have assigned myself to this PR
• [x] PR has an appropriate title: #9999 - What the thing does
• [x] PR has a detailed description, including links to specific documentation
• [x] I have added the appropriate labels to the PR.
• [x] I did not remove any parts of the template, such as checkboxes even if they are not used
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to any documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works. Testing guidelines
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• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] The ticket was moved into the DEV test column when I began testing this change