[Feature-request] Add controls for 'manage overrides' in symbols

[rwlo]

I am a designer and developer, at the beginning stages of updating our existing design system sketch library to a new one with reactsketchapp

We currently use a lot of nested symbols where we set additional rules on the parent symbol to prevent overrides to some child symbols.

Example: Form Label component

This symbol is used within all our form components (inputs, dropdowns, checkboxes, etc.)
I want to use the "manage overrides" feature in sketch to limit what can be overridden on the symbol when nested in parent symbols.

The manage overrides setting in sketch:

Does this exist currently or can we add support for this functionality. Thanks in advance!

[mathieudutour]

blocked by sketch-hq/sketch-file-format-ts#8