Read datadog_host cap variable for specifying Datadog API endpoint

[zippolyte]

What does this PR do?

Closes #230

Description of the Change

Read datadog_host variable for specifying API endpoint

Alternate Designs

Possible Drawbacks

Verification Process

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
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