Implement Multi-Tenant Search Support

[JoseSzycho]

Description

Extend the Search service to operate across virtualized project control planes, enabling federated search across platform and project tenants while maintaining centralized search capabilities as described in the enhancement doc.

[JoseSzycho]

@scotwells I'm already working on implementing a project watcher with an internal tenant registry, and everything seems to be going smoothly.

However, I have a question regarding the NATS queue I'm currently using to capture the event messages. Right now I'm mirroring processor.ExtractTenant() from the Activity repo:

https://github.com/datum-cloud/activity/blob/9cda214fdf3629d869011ccef4723d6cdc7c8716/internal/processor/utils.go#L50-L80

Is that okay? Will that information always be populated? I'm planning to keep using the same AUDIT_EVENTS stream that I was previously using.

I'm just worried about missing something.