feat: Report custom telemetry to Datadog via its OpenTelemetry exporter

[timmc-edx]

This is part of https://github.com/edx/edx-arch-experiments/issues/571

Configuration Pull Request

Make sure that the following steps are done before merging:

• [x] Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• [x] If you are adding any new default values that need to be overridden when this change goes live, update internal repos and add an entry to the top of the CHANGELOG.
• [x] Performed the appropriate testing.
• [x] Think about how this change will affect Open edX operators and update the wiki page for the next Open edX release if needed

[timmc-edx]

Note: This PR is not required if we end up using DatadogBackend.