Use a 1:1 mapping of netbird client to netbird account

- Add debug endpoint for monitoring netbird clients
- Add types package with AccountID type
- Refactor netbird roundtrip to key clients by AccountID
- Multiple domains can share the same client per account
- Add status notifier for tunnel connection updates
- Add OIDC flags to CLI
- Add tests for netbird client management

proxy/internal/types/types.go

@@ -0,0 +1,5 @@
+// Package types defines common types used across the proxy package.
+package types
+
+// AccountID represents a unique identifier for a NetBird account.
+type AccountID string