MDL-42276 core_group: automated testing for MDLQA-1812 and MDLQA-1813

Added behat test for deleting groups/groupings with and without the
'moodle/course:changeidnumber' capability.
MDL-42276 core_behat: added new step definitions to check if an element is readonly or not
MDL-42276 core_group: automated MDLQA-2238 and MDL-2335

Added behat test for updating groups/groupings with and without the
'moodle/course:changeidnumber' capability.
MDL-42276 core_group: automated MDLQA-2105

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