feat: Add Datadog Git Repository Source Code Integration for Edxapp

[nadeemshahzad]

Datadog's source code integration links telemetry to Git repositories. Enabling the integration, we can debug stack traces and other issues by quickly navigating to the relevant lines of code in app repository.
Ticket: https://2u-internal.atlassian.net/browse/GSRE-1686

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Make sure that the following steps are done before merging:

• Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• 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.
• Performed the appropriate testing.