Add text headings and annotations to Observability maps

[sekrish]

Summary

Add Text labels to allow for headings and annotations in the observability maps

Desired Behaviour

Create a text field item that we can drag onto the map to add headings and annotations
NOTE: # ( Tell us how the new feature should work. Be specific. )
TIP: # ( Do NOT give us access or passwords to your New Relic account or API keys! )

Possible Solution

Additional context