Add Domains (formerly Named Clients)

[nicklasl]

Domains allow logical (late) binding of clients with providers, enabling multiple providers in a single application.

Specification References:

• 1.1.3: The API MUST provide a function to bind a given provider to one or more clients using a domain.
• 1.1.6: The API MUST provide a function for creating a client which accepts an optional domain parameter.
• 3.2.2.3: The API MUST have a method for setting evaluation context for a domain.
• 3.2.2.4: The API MUST have a mechanism to manage evaluation context for an associated domain.

Implementation Notes:

• OpenFeatureAPI.setProvider(domain, provider) - Set provider for a domain
• OpenFeatureAPI.setProviderAndWait(domain, provider) - Set provider for a domain (blocking)
• OpenFeatureAPI.getClient(domain) - Get client bound to domain
• OpenFeatureAPI.setContext(domain, context) - Set context for a domain
• Client event handlers should only fire for events from associated provider