[7.x] [APM] generator: support error events and application metrics (#115311)

[kibanamachine]

Backports the following commits to 7.x:

• [APM] generator: support error events and application metrics ([APM] generator: support error events and application metrics #115311)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 4556d51
• Storybooks Preview

Metrics [docs]

Public APIs missing exports

Total count of every type that is part of your API that should be exported but is not. This will cause broken links in the API documentation system. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats exports for more detailed information.

id	before	after	diff
@elastic/apm-generator	2	4	+2

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @dgieselaar