Add isOptional to Checkbox

[jordankoschei-okta]

This PR adds isOptional to Checkbox. In order to make this happen, I needed to use the required prop on FormControlLabel, which necessitated updating to the latest MUI.

[edburyenegren-okta]

1. Should this be wrapped by Field instead? That handles the interactions for our other form fields, though I don't think @KevinGhadyani-Okta has refactored them all.

2. The resulting UI deviates from our other fields, which don't mark required fields as such, instead marking optional fields.

[edburyenegren-okta]

Ah, here's the WIP PR I was thinking of: #1762

[jordankoschei-okta]

Okay, excellent, I can redo this based on the Field refactoring work.

I don't think there's an elegant way of indicating "optional" on a single checkbox, especially since the vast majority of checkboxes will be optional — any thoughts on this?

[jordankoschei-okta]

I made some changes:

1. The asterisk has been replaced with "(Required)"
2. The required text is customizable, for i18n support
3. isOptional is now isRequired for checkboxes

[KevinGhadyani-Okta]

This PR's ready to go, but now we need to integrate with the translation code.