Investigate after-resolution overrides

[ollieread]

Service overrides are currently registered and booted during the boot phase of the framework, which has caused issues where the session override is attempting to make sessions tenant-specific when outside of tenant context (#56). This caused the need for a flag to mark multitenanted context (#57), which could be used within this.

Laravel uses Application::afterResolving() to register view namespaces, as well as several other things.

I think this approach would be beneficial because:

• Service overrides would ONLY be registered IF the relevant service is resolved.
• Service overrides would ONLY be registered IF it's within the multitenanted context when the service is resolved.
• Service overrides would NOT register unnecessarily.
• Service overrides would NOT have the side effect of causing Laravel core services to load.

[ollieread]

This could possibly be achieved by introducing a DeferredServiceOverride that'll only override a service when X, or X, Y.... have been resolved.