Assign merge candidate tests

n/n	description	inputs	expected result GraphQl
ASM1	Assign merge candidate without scopes	token	missing allowance merge_candidate:assign
ASM2	Assign merge candidate without role	doctor token	403, FORBIDDEN
ASM3	Assign merge candidate with client not NHS	token invalid client id	403, FORBIDDEN
ASM4	Assign MR already have one in status NEW	token	CONFLICT, Assignee is not allowed to ask for new merge request
ASM5	Assign MR to User which already has POSTPONE >=postponed_requests_limit	token	CONFLICT, Assignee reached limit in postponed merge_requests
ASM6	Assign MR in case there is no left one NEW and not viewed by User merge candidate in DB	token	204, No content
ASM7	Assign new MR to User	token	Merge Request is assigned manual_merge_candidates. assignee_id=user_id there is a row in merge_requests with user_id+merge_candidate_id and status=NEW there is a row in audit_log with status=NEW