Standardise zipkin and prometheus exporter component type names

[JonasKunz]

Adds component type names for prometheus and Zipkin exporters to be used in SDK health metrics.

Both Zipkin and Prometheus are explicitly supported in the SDK specification, so it makes sense to add those.

Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] schema-next.yaml updated with changes to existing conventions.