MDL-42276 core_group: automated testing for MDLQA-1812

Added behat test for deleting groups/groupings.
MDL-42276 core_behat: added new step definition to check if one element exists in another
MDL-42276 core_group: replaces need for MDLQA-1813

Added behat test for deleting groups/groupings without 'moodle/course:changeidnumber' capability.
MDL-42276 core_behat: added new step definition to check that an element is readonly
MDL-42276 core_group: replaces need for MDLQA-2105

Added behat test for creating groups/groupings without 'moodle/course:changeidnumber' capability.
MDL-42276 core_group: replaced need for MDLQA-2238

Added behat test for updating groups/groupings without 'moodle/course:changeidnumber' capability.