Add origin_detection_enabled support for datadog backend (#108)

[willkg]

This adds origin_detection_enabled support and defaults it to False which works better if you're not using the Datadog agent.

This ups the datadog dependency to 0.45.0 which is the version that added the container id stuff, or higher. I thought about making the code support <0.45.0 and >=0.45.0, but then decided not to. If that turns out to be an error, we can add support later. I'll make sure to call it out in the notes and maybe even consider it a backwards-incompatible change causing me to increase the major version.

Fixes #108

[willkg]

@jwhitlock Can you review this? Does this look ok?

[willkg]

Thank you!