[exporter/datadog] Adds support for sending metric origin

[mx-psi]

Description:

Adds support for sending metrics origin. Full support is added for sketches, partial support for all other metrics since the origin_category and origin_service fields may suffer a rename. To do this:

• Updates opentelemetry-mapping-go to include [pkg/otlp/metrics] Initial support for metrics origin DataDog/opentelemetry-mapping-go#204
• Updates agent-payload to include Add metrics origin product, service and category DataDog/agent-payload#280
• Update api-client consumer to set metrics origin
• Update legacy consumer to set metrics origin (only on the sketches)

This is a no-op since the real work will be done on DataDog/opentelemetry-mapping-go/pull/203, but this is blocked on support int the backend for this. Thus I am skipping changelog and will add an actual changelog on the other PR.

To avoid depending on DataDog/datadog-api-client-go/pull/2299, we use the AdditionalProperties field that gets added during marshaling.

[mx-psi]

cc @joepin would like to verify that sending origin_product is okay since this one will not incur any renames.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.