Is your feature request related to a problem? Please describe.
We add a small amount of default padding (1px) to axis tick labels to help with discrepancies in browser canvas text measurement. Users might want to themselves be able to adjust the amount of padding for a tick label, which is what is proposed here.

Describe the solution you'd like
Add tick label padding to the axis spec and use this to adjust the computed bounding box dimensions for a tick label.

Describe alternatives you've considered
n/a

Additional context
n/a

Kibana Cross Issues
n/a

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