captureError sending labels not working

Description: Adding labels to error through `captureError(Error, { labels: ...})` doesn't work because they are ignored when are send to server because only labels/tags from configService in [createMetadata](https://github.com/elastic/apm-agent-rum-js/blob/main/packages/rum-core/src/common/apm-server.js#L325) function are taken into consideration. Expected result: `options.label` labels added in `captureError` function call are send to server Related Issue: #1591