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/repository/instance/domain.go

@@ -13,6 +13,10 @@ const (
 	InstanceDomainAddedEventType      = domainEventPrefix + "added"
 	InstanceDomainPrimarySetEventType = domainEventPrefix + "primary.set"
 	InstanceDomainRemovedEventType    = domainEventPrefix + "removed"
+
+	InstanceDomainSearchType     = "instance_domain"
+	InstanceDomainSearchField    = "domain"
+	InstanceDomainObjectRevision = uint8(1)
 )
 
 func NewAddInstanceDomainUniqueConstraint(domain string) *eventstore.UniqueConstraint {
@@ -43,6 +47,30 @@ func (e *DomainAddedEvent) UniqueConstraints() []*eventstore.UniqueConstraint {
 	return []*eventstore.UniqueConstraint{NewAddInstanceDomainUniqueConstraint(e.Domain)}
 }
 
+func (e *DomainAddedEvent) Fields() []*eventstore.FieldOperation {
+	return []*eventstore.FieldOperation{
+		eventstore.SetField(
+			e.Aggregate(),
+			domainSearchObject(e.Domain),
+			InstanceDomainSearchField,
+			&eventstore.Value{
+				Value: e.Domain,
+				// TODO: (adlerhurst) ensure uniqueness if we go with fields table: https://github.com/zitadel/zitadel/issues/9009
+				MustBeUnique: false,
+				ShouldIndex:  true,
+			},
+
+			eventstore.FieldTypeInstanceID,
+			eventstore.FieldTypeResourceOwner,
+			eventstore.FieldTypeAggregateType,
+			eventstore.FieldTypeAggregateID,
+			eventstore.FieldTypeObjectType,
+			eventstore.FieldTypeObjectID,
+			eventstore.FieldTypeFieldName,
+		),
+	}
+}
+
 func NewDomainAddedEvent(ctx context.Context, aggregate *eventstore.Aggregate, domain string, generated bool) *DomainAddedEvent {
 	return &DomainAddedEvent{
 		BaseEvent: *eventstore.NewBaseEventForPush(
@@ -118,6 +146,29 @@ func (e *DomainRemovedEvent) UniqueConstraints() []*eventstore.UniqueConstraint
 	return []*eventstore.UniqueConstraint{NewRemoveInstanceDomainUniqueConstraint(e.Domain)}
 }
 
+func (e *DomainRemovedEvent) Fields() []*eventstore.FieldOperation {
+	return []*eventstore.FieldOperation{
+		eventstore.SetField(
+			e.Aggregate(),
+			domainSearchObject(e.Domain),
+			InstanceDomainSearchField,
+			&eventstore.Value{
+				Value:        e.Domain,
+				MustBeUnique: true,
+				ShouldIndex:  true,
+			},
+
+			eventstore.FieldTypeInstanceID,
+			eventstore.FieldTypeResourceOwner,
+			eventstore.FieldTypeAggregateType,
+			eventstore.FieldTypeAggregateID,
+			eventstore.FieldTypeObjectType,
+			eventstore.FieldTypeObjectID,
+			eventstore.FieldTypeFieldName,
+		),
+	}
+}
+
 func NewDomainRemovedEvent(ctx context.Context, aggregate *eventstore.Aggregate, domain string) *DomainRemovedEvent {
 	return &DomainRemovedEvent{
 		BaseEvent: *eventstore.NewBaseEventForPush(
@@ -140,3 +191,11 @@ func DomainRemovedEventMapper(event eventstore.Event) (eventstore.Event, error)
 
 	return domainRemoved, nil
 }
+
+func domainSearchObject(domain string) eventstore.Object {
+	return eventstore.Object{
+		Type:     InstanceDomainSearchType,
+		ID:       domain,
+		Revision: InstanceDomainObjectRevision,
+	}
+}

internal/repository/instance/instance.go

@@ -106,6 +106,14 @@ func (e *InstanceRemovedEvent) UniqueConstraints() []*eventstore.UniqueConstrain
 	return constraints
 }
 
+func (e *InstanceRemovedEvent) Fields() []*eventstore.FieldOperation {
+	return []*eventstore.FieldOperation{
+		eventstore.RemoveSearchFields(map[eventstore.FieldType]any{
+			eventstore.FieldTypeInstanceID: e.Aggregate().ID,
+		}),
+	}
+}
+
 func NewInstanceRemovedEvent(ctx context.Context, aggregate *eventstore.Aggregate, name string, domains []string) *InstanceRemovedEvent {
 	return &InstanceRemovedEvent{
 		BaseEvent: *eventstore.NewBaseEventForPush(