perf(import): optimize search for domains claimed by other organizations (#8200)

# Which Problems Are Solved

Improve the performance of human imports by optimizing the query that
finds domains claimed by other organizations.

# How the Problems Are Solved

Use the fields search table introduced in
https://github.com/zitadel/zitadel/pull/8191 by storing each
organization domain as Object ID and the verified status as field value.

# Additional Changes

- Feature flag for this optimization

# Additional Context

- Performance improvements for import are evaluated and acted upon
internally at the moment

---------

Co-authored-by: adlerhurst <silvan.reusser@gmail.com>

internal/query/projection/eventstore_field.go

@@ -7,13 +7,32 @@ import (
 	"github.com/zitadel/zitadel/internal/repository/project"
 )
 
+const (
+	fieldsProjectGrant      = "project_grant_fields"
+	fieldsOrgDomainVerified = "org_domain_verified_fields"
+)
+
 func newFillProjectGrantFields(config handler.Config) *handler.FieldHandler {
 	return handler.NewFieldHandler(
 		&config,
-		"project_grant_fields",
+		fieldsProjectGrant,
 		map[eventstore.AggregateType][]eventstore.EventType{
 			org.AggregateType:     nil,
 			project.AggregateType: nil,
 		},
 	)
 }
+
+func newFillOrgDomainVerifiedFields(config handler.Config) *handler.FieldHandler {
+	return handler.NewFieldHandler(
+		&config,
+		fieldsOrgDomainVerified,
+		map[eventstore.AggregateType][]eventstore.EventType{
+			org.AggregateType: {
+				org.OrgDomainAddedEventType,
+				org.OrgDomainVerifiedEventType,
+				org.OrgDomainRemovedEventType,
+			},
+		},
+	)
+}