[Meta] Make composite field an alternative to paragraphs

I definitely think (agree with Slack discussions) that to gain widespread adoption the ability to add a field to an existing composite field would bring it to some feature parity with paragraphs for site building.

This would add a new column(s) to the table, and so if say, the field was required or needed a default value, then the module would need to backfill the column for existing rows. Note that Paragraphs doesn't do a retrospective back-filling so I consider this partially supported by Paragraphs. Whe you add a field to a paragraph it adds a new table which is initially empty, but for this module I don't think this is a going to cut it.

As noted in slack, a dependency will be CRUD operations for field types ✨ Field type modules cannot maintain their field schema (field type schema change C(R)UD is needed) Needs work