Management of patients with germline predisposition to haematological malignancies considered for allogeneic blood and marrow transplantation: Best practice consensus guidelines from the <scp>UK</scp> Cancer Genetics Group ( <scp>UKCGG</scp> ), <scp>CanGene‐CanVar</scp> , <scp>NHS</scp> England Genomic Laboratory Hub ( <scp>GLH</scp> ) Haematological Malignancies Working Group and the British Society of Blood and Marrow Transplantation and cellular therapy ( <scp>BSBMTCT</scp> )