Add runtime metrics

[liyanwei93]

Changes

Add runtime metrics in golang application and nodejs application for demo purpose.

Merge Requirements

For new features contributions please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[morningspace]

When adding these runtime metrics, can we follow the semcov spec from community?
https://opentelemetry.io/docs/specs/semconv/runtime/go-metrics/#go-goroutines.
The same applies to node.js.

For example: go_goroutines, it is represented as go.goroutine.count in community semcov.

[morningspace]

For the purpose of completeness, besides Checkout Service, we probably also need to handle Product Catalog Service as another golang app by adding runtime metrics monitoring.

With that, shall we move runtime metrics monitoring code to a separate place so that can be reused by both two services?

[morningspace]

I'm thinking whether this should move to a separate folder, e.g.: /instana, just as Petr did, so that it's easy to merge updates from upstream later. The /instana folder can host any changes specific to Instana, including sample configuration, documents, etc.