Duplicate New Relic Dashboard and Alert search script for Datadog

[robrap]

AC:

• Implement datadog_search.py to duplicate new_relic_search.py (adjusted for differences in tooling)
• Communicate widely.

We had a search script for NRQL in New Relic alerts and dashboards: https://github.com/openedx/edx-django-utils/blob/master/edx_django_utils/monitoring/scripts/new_relic_search.py.

This is very useful when changing names of teams or services or custom attributes, because you need to know about usage.

Here is a doc for monitor search in DD: https://docs.datadoghq.com/api/latest/monitors/#monitors-search

[robrap]

Note: If we decide to rename the lms workers, again this script would be useful.