Configurable request timeout

Currently, there is no request timeout set in SchemaAppCache::cdnGet() which leads to \Drupal::httpClient()'s default 30 second timeout to be used which leads to blocking the main request that is serving the Drupal page when the schemaapp.com is slow or un-responsive.

Updates needed:
* Add a request timeout to the module's configuration. Default: 30 sec or lower. Sites can lower as needed, example 5 sec.
* Use the request timeout config in SchemaAppCache::cdnGet() when performing the request.