[APM] No APM data showing up in Kibana APM UI

[simitt]

Kibana version

8.0.0-SNAPSHOT

APM Server version (if applicable)

8.0.0-SNAPSHOT

Elasticsearch version (if applicable)

No response

Steps to Reproduce

0. Start ES, Kibana and APM Server 8.0.0-SNAPSHOT (for example on Cloud QA, or with apm-integration-testing)
1. Install APM Integration (current version 8.0.0-dev4)
2. Ingest data into APM Server, for example download example payload and send it to your APM Server,
   for example via curl curl -i -k -H "Content-type: application/x-ndjson" -H "Authorization: Bearer ${APM_SERVER_TOKEN}" --data-binary @testdata/intake-v2/events.ndjson ${APM_SERVER_URL}/intake/v2/events
3. Ensure that the data have been indexed by the APM Server by checking that GET traces-apm*/_search contains documents.

4. Observe that no APM data are showing up in the UI

Expected Behavior

APM UI should show ingested data

Actual Behavior

APM UI is not showing APM data, but the Welcome page:

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[simitt]

Closing as duplicate of #121164