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/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(