CloudWatch: Add additional AWS/SageMaker metrics

[tristanburgess]

This is part of https://github.com/grafana/cloud-onboarding/issues/6236

What is this feature?

This adds SageMaker metrics for all namespaces except for GroundTruth and FeatureStore, which our customer did not seem to have a need for.

Why do we need this feature?

Per the above linked ticket, we have customers that are interested in several SageMaker namespaces that we do not currently have support for

Who is this feature for?

AWS SageMaker users for the CW Integration and/or DataSource

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.