[LineAnnotation] Improve label overlapping

[nickofthyme]

Is your feature request related to a problem? Please describe.
Currently we don't have any logic to avoid collisions when rendering line annotation labels.

Describe the solution you'd like

• Annotations should know about each other and adapt label placement.
• Annotations should collapse into a group when too close.

Additional context
Lens currently has logic to group annotations that are too close to avoid overlapping annotation icons, dynamic text labels would be much harder to solve.

Kibana Cross Issues
elastic/kibana#233323

Checklist

• this request is checked against already exist requests
• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present