* Fix performance issues in system config when viewing total counts for the abandoned cart syncs (for large datasets) - use collection->getSize() instead of loading the whole collection and performing a count.
* Change admin config sorting so that the extension shows near the bottom of the system config tabs and is not the default viewing config.
* Fix performance issues in system config when viewing total counts for the customer and order syncs (for large datasets) - use search and filter builder instead of loading the whole collection and performing a count.
* Update JSON serializer in curl helper. Move optional parameter to bottom of constructor args (Fixes potential issues when creating a customer via API or GraphQL). Check if response is of type array in getMessage since the response is of mixed type. Cleanup: remove unnecessary double quotes, update doc blocks, fix PHPCS and PHPMD issues. Added Todo's.
