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/projection.go

@@ -83,6 +83,7 @@ var (
 
 	ProjectGrantFields      *handler.FieldHandler
 	OrgDomainVerifiedFields *handler.FieldHandler
+	InstanceDomainFields    *handler.FieldHandler
 )
 
 type projection interface {
@@ -170,6 +171,7 @@ func Create(ctx context.Context, sqlClient *database.DB, es handler.EventStore,
 
 	ProjectGrantFields = newFillProjectGrantFields(applyCustomConfig(projectionConfig, config.Customizations[fieldsProjectGrant]))
 	OrgDomainVerifiedFields = newFillOrgDomainVerifiedFields(applyCustomConfig(projectionConfig, config.Customizations[fieldsOrgDomainVerified]))
+	InstanceDomainFields = newFillInstanceDomainFields(applyCustomConfig(projectionConfig, config.Customizations[fieldsInstanceDomain]))
 
 	newProjectionsList()
 	return nil