refactor(v2): init events (#7823)

creates events structures for initial projections and read models

internal/v2/user/username_changed.go

@@ -0,0 +1,37 @@
+package user
+
+import (
+	"github.com/zitadel/zitadel/internal/v2/eventstore"
+	"github.com/zitadel/zitadel/internal/zerrors"
+)
+
+type usernameChangedPayload struct {
+	Username string `json:"userName"`
+}
+
+type UsernameChangedEvent eventstore.Event[usernameChangedPayload]
+
+const UsernameChangedType = AggregateType + ".username.changed"
+
+var _ eventstore.TypeChecker = (*UsernameChangedEvent)(nil)
+
+// ActionType implements eventstore.Typer.
+func (c *UsernameChangedEvent) ActionType() string {
+	return UsernameChangedType
+}
+
+func UsernameChangedEventFromStorage(event *eventstore.StorageEvent) (e *UsernameChangedEvent, _ error) {
+	if event.Type != e.ActionType() {
+		return nil, zerrors.ThrowInvalidArgument(nil, "USER-hCGsh", "Errors.Invalid.Event.Type")
+	}
+
+	payload, err := eventstore.UnmarshalPayload[usernameChangedPayload](event.Payload)
+	if err != nil {
+		return nil, err
+	}
+
+	return &UsernameChangedEvent{
+		StorageEvent: event,
+		Payload:      payload,
+	}, nil
+}