feat(v3alpha): write actions (#8225)

# Which Problems Are Solved

The current v3alpha actions APIs don't exactly adhere to the [new
resources API
design](https://zitadel.com/docs/apis/v3#standard-resources).

# How the Problems Are Solved

- **Breaking**: The current v3alpha actions APIs are removed. This is
breaking.
- **Resource Namespace**: New v3alpha actions APIs for targets and
executions are added under the namespace /resources.
- **Feature Flag**: New v3alpha actions APIs still have to be activated
using the actions feature flag
- **Reduced Executions Overhead**: Executions are managed similar to
settings according to the new API design: an empty list of targets
basically makes an execution a Noop. So a single method, SetExecution is
enough to cover all use cases. Noop executions are not returned in
future search requests.
- **Compatibility**: The executions created with previous v3alpha APIs
are still available to be managed with the new executions API.

# Additional Changes

- Removed integration tests which test executions but rely on readable
targets. They are added again with #8169

# Additional Context

Closes #8168

internal/repository/execution/execution.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/zitadel/zitadel/internal/domain"
 	"github.com/zitadel/zitadel/internal/eventstore"
+	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
 const (
@@ -56,6 +57,13 @@ type Target struct {
 	Target string                     `json:"target"`
 }
 
+func (t *Target) Validate() error {
+	if t.Type == domain.ExecutionTargetTypeUnspecified || t.Target == "" {
+		return zerrors.ThrowInvalidArgument(nil, "COMMAND-hdm4zl1hmd", "Errors.Execution.Invalid")
+	}
+	return nil
+}
+
 func NewSetEventV2(
 	ctx context.Context,
 	aggregate *eventstore.Aggregate,