feat: implement instance-level UpdateZitadelProvider (#12378)

# Which Problems Are Solved

This PR implements the instance-level `UpdateZitadelProvider` endpoint,
enabling updates to existing instance Zitadel IdP templates.

# How the Problems Are Solved

- Added `AdminService.UpdateZitadelProvider` handler, converter
- Added the command-layer implementation to update a ZitadelProvider and
push `instance.idp.zitadel.changed` event
- Added projection-layer implementation to persist Zitadel provider
updates into `projections.idp_templates6_zitadel`
- Added unit and integration tests


# Additional Changes
N/A

# Additional Context
Related to https://github.com/zitadel/zitadel/issues/11922
Follow-up for PRs:
- https://github.com/zitadel/zitadel/pull/12018
- https://github.com/zitadel/zitadel/pull/12020
- https://github.com/zitadel/zitadel/pull/12055
- https://github.com/zitadel/zitadel/pull/12056
- https://github.com/zitadel/zitadel/pull/12371

---------

Co-authored-by: Copilot Autofix powered by AI <[email protected]>

internal/command/instance_idp_model.go

@@ -1058,6 +1058,8 @@ func (wm *InstanceZitadelIDPWriteModel) AppendEvents(events ...eventstore.Event)
 		switch e := event.(type) {
 		case *instance.ZitadelIDPAddedEvent:
 			wm.ZitadelIDPWriteModel.AppendEvents(&e.ZitadelIDPAddedEvent)
+		case *instance.ZitadelIDPChangedEvent:
+			wm.ZitadelIDPWriteModel.AppendEvents(&e.ZitadelIDPChangedEvent)
 		default:
 			wm.ZitadelIDPWriteModel.AppendEvents(e)
 		}
@@ -1076,3 +1078,29 @@ func (wm *InstanceZitadelIDPWriteModel) Query() *eventstore.SearchQueryBuilder {
 		EventData(map[string]interface{}{"id": wm.ID}).
 		Builder()
 }
+
+func (wm *InstanceZitadelIDPWriteModel) NewChangedEvent(
+	ctx context.Context,
+	aggregate *eventstore.Aggregate,
+	id, name, issuer, clientID, clientSecretString string,
+	secretCrypto crypto.EncryptionAlgorithm,
+	scopes []string,
+	options idp.Options,
+	info []idp.RolesInfo,
+) (*instance.ZitadelIDPChangedEvent, error) {
+
+	changes, err := wm.NewChanges(
+		name,
+		issuer,
+		clientID,
+		clientSecretString,
+		secretCrypto,
+		scopes,
+		options,
+		info,
+	)
+	if err != nil || len(changes) == 0 {
+		return nil, err
+	}
+	return instance.NewZitadelIDPChangedEvent(ctx, aggregate, id, changes), nil
+}