[Feature] Update LD set up changes

[thetif]

Description and related issues

When talking to MC-Review, we learned that you can access a ldClient variable anywhere in the code. If this variable is available in Redux, we can remove the setFlag action and the watcher in Root.

They also used a const file that contained all of their flags. Create a flag file and update the code to use those consts instead of strings. For example:

export const featureFlags = {
	NEW_TESTING_FLAG: {
		flag: 'new-testing-flag',
		defaultValue: true
	}
}

This task is done when…

• [ ] ldClient has replaced our current redux solution
• [ ] all have constants in the @cms-eapd/common package
• [ ] all references to flags are using the constants created above