Simplified flagd feature flag configuration

[toddbaert]

The current flagd flag configuration schema lacks some reasonable defaults that can easily be derived assumed:

• Boolean flags don't really need variants explicitly defined - they essentially should always be true/false. We can make these variants "implied".
• Flags states are generally ENABLED. We should implicitly assume they are ENABLED if the state is not defined.

Things that need to be done to accomplish this:

• Relax JSON schema to support this.
• Leverage relaxed schema in flagd and make required updates to state management to support this
• Leverage relaxed schema in OFO

[beeme1mr]

We'll need to update the schema store and the default variants should only be "true" or "false" when the variant property is omitted.