* added customer cache && refactored assign/unassing to/from customer nodes
* refactoring of customer action nodes & added common tests
* added tests for upgrade
* updated controller & service tests for customer api
* replaced findCustomerByTenantIdAndTitle with cacheable method
* add new line to end of ../upgrade/3.6.2/schema_update.sql file
* added cache for find user by tenant id and email & relation action nodes refactoring
* fixed synchronization issue & refactored logic & refactored node upgrade tests
* fixed testSaveUserWithSameEmail test in the UserControllerTest. Removed empty space & added exclamation mark
* updated tests for create relation node && added two tests for delete relation node
* replaced Lists with EnumSets where it was possible & replaced MethodSource with EnumSource where it was possible & added test for upgrade for both create and delete relation nodes
* updated upgrade tests & added tests for delete relation node
* refactoring
* updated create & delete relation nodes descriptions
* updated default config for delete relation node
* minor improvements for custom action nodes after self review
* added upgrade for customers with the same titles
* replaced parameterized test annotation when deleteForSingleEntity is false
* fix typo in reSaveCustomerWithNewTitle upgrade logic
* fixes after review & additional improvements
* fixed testAssignAndUnassignEntityViewToCustomer test
* updated upgrade logic & changed logic of public customers lookup
* fixed dao method & added test
* renamed method to findPublicCustomerByTenantId
* fix typo in the find public customer query
* added @Serial annotation for serialVersionUID & rollback saveAndFlush to save in UserServiceImpl
* fixes to async find or create logic
* fixed after review
* fix typo
* set Transactional annotation to findOrCreatePublicCustomer
