Add support for `default`

[travjenkins]

Based on rename and redact

This should look and act almost identical to how rename and redact work.

General workflow

A CTA of some kind of each field
Clicking it opens a modal
That modal gives the user the ability to provide a default
This default is not added until the user clicks "apply" cta
If they want to remove probably force to open modal and remove then "apply" again

Docs

https://docs.estuary.dev/concepts/schemas/#default-annotations

[travjenkins]

Putting this back for now. We are going to put more focus on making the current features (redact / rename) easier for the user to discover.