fix: prevent possible nil pointer panics (#11728)

# Which Problems Are Solved

We found multiple cases where potentially a panic occurred or could
occur:
- when de/encrypting certain information
- returning apps without any configuration type (?)
- apple IdPs without a proper private key

# How the Problems Are Solved

- Added nil checks
- Check private key format for apple IdPs
- Added necessary helper function

# Additional Changes

Fixed i18n yaml where the IDP errors were indented under `org` instead
of directly under `errors`.

# Additional Context

- requires backport to v4.x

---------

Co-authored-by: Marco A. <[email protected]>

internal/api/grpc/project/application.go

@@ -38,7 +38,10 @@ func AppConfigToPb(app *query.App) app_pb.AppConfig {
 	if app.SAMLConfig != nil {
 		return AppSAMLConfigToPb(app.SAMLConfig)
 	}
-	return AppAPIConfigToPb(app.APIConfig)
+	if app.APIConfig != nil {
+		return AppAPIConfigToPb(app.APIConfig)
+	}
+	return nil
 }
 
 func AppOIDCConfigToPb(app *query.OIDCApp) *app_pb.App_OidcConfig {