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

cmd/setup/setup.go

@@ -171,6 +171,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 	steps.s38BackChannelLogoutNotificationStart = &BackChannelLogoutNotificationStart{dbClient: esPusherDBClient, esClient: eventstoreClient}
 	steps.s39DeleteStaleOrgFields = &DeleteStaleOrgFields{dbClient: esPusherDBClient}
 	steps.s40InitPushFunc = &InitPushFunc{dbClient: esPusherDBClient}
+	steps.s41FillFieldsForInstanceDomains = &FillFieldsForInstanceDomains{eventstore: eventstoreClient}
 
 	err = projection.Create(ctx, projectionDBClient, eventstoreClient, config.Projections, nil, nil, nil)
 	logging.OnError(err).Fatal("unable to start projections")
@@ -218,6 +219,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 		steps.s35AddPositionToIndexEsWm,
 		steps.s36FillV2Milestones,
 		steps.s38BackChannelLogoutNotificationStart,
+		steps.s41FillFieldsForInstanceDomains,
 	} {
 		mustExecuteMigration(ctx, eventstoreClient, step, "migration failed")
 	}