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 <46600784+stebenz@users.noreply.github.com>
(cherry picked from commit a9ebc06c77)

internal/eventstore/v3/mock_test.go

@@ -47,6 +47,10 @@ func (e *mockCommand) Fields() []*eventstore.FieldOperation {
 }
 
 func mockEvent(aggregate *eventstore.Aggregate, sequence uint64, payload Payload) eventstore.Event {
+	return mockEventType(aggregate, sequence, payload, "event.type")
+}
+
+func mockEventType(aggregate *eventstore.Aggregate, sequence uint64, payload Payload, typ string) eventstore.Event {
 	return &event{
 		command: &command{
 			InstanceID:    aggregate.InstanceID,
@@ -55,7 +59,7 @@ func mockEvent(aggregate *eventstore.Aggregate, sequence uint64, payload Payload
 			Owner:         aggregate.ResourceOwner,
 			Creator:       "creator",
 			Revision:      1,
-			CommandType:   "event.type",
+			CommandType:   typ,
 			Payload:       payload,
 		},
 		sequence: sequence,