Add Multitenancy Support to ash_phoenix.gen.live & ash_phoenix.gen.html

[jeffhuen]

Currently, mix ash_phoenix.gen.live does not natively support multitenancy. For users building SaaS applications with Ash and AshPostgres, handling multitenancy requires manual intervention.

Generated LiveView pages do not automatically respect tenant context, requiring additional modifications to:
• Ensure LiveView sessions and queries include tenant information.
• Modify mount/3 in generated LiveViews to retrieve and apply the correct tenant.
• Adjust the router to properly assign tenants for multitenant-aware resources.

Without first-class support for multitenancy in ash_phoenix.gen.live, developers need to manually patch these issues every time they generate a new resource.