refactor(handler): cache active instances (#9008)

# Which Problems Are Solved

Scheduled handlers use `eventstore.InstanceIDs` to get the all active
instances within a given timeframe. This function scrapes through all
events written within that time frame which can cause heavy load on the
database.

# How the Problems Are Solved

A new query cache `activeInstances` is introduced which caches the ids
of all instances queried by id or host within the configured timeframe.

# Additional Changes

- Changed `default.yaml`
  - Removed `HandleActiveInstances` from custom handler configs
- Added `MaxActiveInstances` to define the maximal amount of cached
instance ids
- fixed start-from-init and start-from-setup to start auth and admin
projections twice
- fixed org cache invalidation to use correct index

# Additional Context

- part of #8999

internal/query/instance.go

@@ -143,6 +143,10 @@ func (q *InstanceSearchQueries) toQuery(query sq.SelectBuilder) sq.SelectBuilder
 	return query
 }
 
+func (q *Queries) ActiveInstances() []string {
+	return q.caches.activeInstances.Keys()
+}
+
 func (q *Queries) SearchInstances(ctx context.Context, queries *InstanceSearchQueries) (instances *Instances, err error) {
 	ctx, span := tracing.NewSpan(ctx)
 	defer func() { span.EndWithError(err) }()
@@ -198,10 +202,13 @@ var (
 )
 
 func (q *Queries) InstanceByHost(ctx context.Context, instanceHost, publicHost string) (_ authz.Instance, err error) {
+	var instance *authzInstance
 	ctx, span := tracing.NewSpan(ctx)
 	defer func() {
 		if err != nil {
 			err = fmt.Errorf("unable to get instance by host: instanceHost %s, publicHost %s: %w", instanceHost, publicHost, err)
+		} else {
+			q.caches.activeInstances.Add(instance.ID, true)
 		}
 		span.EndWithError(err)
 	}()
@@ -225,6 +232,12 @@ func (q *Queries) InstanceByHost(ctx context.Context, instanceHost, publicHost s
 func (q *Queries) InstanceByID(ctx context.Context, id string) (_ authz.Instance, err error) {
 	ctx, span := tracing.NewSpan(ctx)
 	defer func() { span.EndWithError(err) }()
+	defer func() {
+		if err != nil {
+			return
+		}
+		q.caches.activeInstances.Add(id, true)
+	}()
 
 	instance, ok := q.caches.instance.Get(ctx, instanceIndexByID, id)
 	if ok {