Afform - WIP action modes for joins

[colemanw]

Overview

WIP idea for an "Allowed Actions" for joins in Afform
Fixes dev/core#5589

Before

The main entity supports lets you enable/disable actions, but not the joined entities (email, address, phone, multi-record custom data). Those are currently set to allow create+update+delete.

After

Can disable update & delete actions if desired (if both are unchecked, only create is allowed).

[civibot]

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