perf(actionsv2): execution target router (#10564)

# Which Problems Are Solved

The event execution system currently uses a projection handler that
subscribes to and processes all events for all instances. This creates a
high static cost because the system over-fetches event data, handling
many events that are not needed by most instances. This inefficiency is
also reflected in high "rows returned" metrics in the database.

# How the Problems Are Solved

Eliminate the use of a project handler. Instead, events for which
"execution targets" are defined, are directly pushed to the queue by the
eventstore. A Router is populated in the Instance object in the authz
middleware.

- By joining the execution targets to the instance, no additional
queries are needed anymore.
- As part of the instance object, execution targets are now cached as
well.
- Events are queued within the same transaction, giving transactional
guarantees on delivery.
- Uses the "insert many fast` variant of River. Multiple jobs are queued
in a single round-trip to the database.
- Fix compatibility with PostgreSQL 15

# Additional Changes

- The signing key was stored as plain-text in the river job payload in
the DB. This violated our [Secrets
Storage](https://zitadel.com/docs/concepts/architecture/secrets#secrets-storage)
principle. This change removed the field and only uses the encrypted
version of the signing key.
- Fixed the target ordering from descending to ascending.
- Some minor linter warnings on the use of `io.WriteString()`.

# Additional Context

- Introduced in https://github.com/zitadel/zitadel/pull/9249
- Closes https://github.com/zitadel/zitadel/issues/10553
- Closes https://github.com/zitadel/zitadel/issues/9832
- Closes https://github.com/zitadel/zitadel/issues/10372
- Closes https://github.com/zitadel/zitadel/issues/10492

---------

Co-authored-by: Stefan Benz <[email protected]>

internal/execution/projections.go

@@ -3,10 +3,8 @@ package execution
 import (
 	"context"
 
-	"github.com/zitadel/zitadel/internal/eventstore"
+	"github.com/zitadel/zitadel/internal/crypto"
 	"github.com/zitadel/zitadel/internal/eventstore/handler/v2"
-	"github.com/zitadel/zitadel/internal/query"
-	"github.com/zitadel/zitadel/internal/query/projection"
 	"github.com/zitadel/zitadel/internal/queue"
 )
 
@@ -15,18 +13,12 @@ var (
 )
 
 func Register(
-	ctx context.Context,
-	executionsCustomConfig projection.CustomConfig,
 	workerConfig WorkerConfig,
-	queries *query.Queries,
-	eventTypes []string,
 	queue *queue.Queue,
+	targetEncAlg crypto.EncryptionAlgorithm,
 ) {
 	queue.ShouldStart()
-	projections = []*handler.Handler{
-		NewEventHandler(ctx, projection.ApplyCustomConfig(executionsCustomConfig), eventTypes, eventstore.AggregateTypeFromEventType, queries, queue),
-	}
-	queue.AddWorkers(NewWorker(workerConfig))
+	queue.AddWorkers(NewWorker(workerConfig, targetEncAlg))
 }
 
 func Start(ctx context.Context) {