feat: actions v2 execution targets command side (#7384)

Adds the API to create, update, delete targets for execution in a new ExecutionService (v3alpha)

internal/domain/target.go

@@ -0,0 +1,28 @@
+package domain
+
+type TargetType uint
+
+const (
+	TargetTypeUnspecified TargetType = iota
+	TargetTypeWebhook
+	TargetTypeRequestResponse
+
+	TargetTypeStateCount
+)
+
+type TargetState int32
+
+const (
+	TargetUnspecified TargetState = iota
+	TargetActive
+	TargetRemoved
+	targetStateCount
+)
+
+func (s TargetState) Valid() bool {
+	return s >= 0 && s < targetStateCount
+}
+
+func (s TargetState) Exists() bool {
+	return s != TargetUnspecified && s != TargetRemoved
+}