feat(fields): add instance domain (#9000)

# Which Problems Are Solved

Instance domains are only computed on read side. This can cause missing
domains if calls are executed shortly after a instance domain (or
instance) was added.

# How the Problems Are Solved

The instance domain is added to the fields table which is filled on
command side.

# Additional Changes

- added setup step to compute instance domains
- instance by host uses fields table instead of instance_domains table

# Additional Context

- part of https://github.com/zitadel/zitadel/issues/8999

internal/query/projection/eventstore_field.go

@@ -3,6 +3,7 @@ package projection
 import (
 	"github.com/zitadel/zitadel/internal/eventstore"
 	"github.com/zitadel/zitadel/internal/eventstore/handler/v2"
+	"github.com/zitadel/zitadel/internal/repository/instance"
 	"github.com/zitadel/zitadel/internal/repository/org"
 	"github.com/zitadel/zitadel/internal/repository/project"
 )
@@ -10,6 +11,7 @@ import (
 const (
 	fieldsProjectGrant      = "project_grant_fields"
 	fieldsOrgDomainVerified = "org_domain_verified_fields"
+	fieldsInstanceDomain    = "instance_domain_fields"
 )
 
 func newFillProjectGrantFields(config handler.Config) *handler.FieldHandler {
@@ -36,3 +38,17 @@ func newFillOrgDomainVerifiedFields(config handler.Config) *handler.FieldHandler
 		},
 	)
 }
+
+func newFillInstanceDomainFields(config handler.Config) *handler.FieldHandler {
+	return handler.NewFieldHandler(
+		&config,
+		fieldsInstanceDomain,
+		map[eventstore.AggregateType][]eventstore.EventType{
+			instance.AggregateType: {
+				instance.InstanceDomainAddedEventType,
+				instance.InstanceDomainRemovedEventType,
+				instance.InstanceRemovedEventType,
+			},
+		},
+	)
+}