Update the YAML schema in the gwas-sumstat-tools

[jiyue1214]

genome_assembly and file_type are crucial fields for the harmonisation pipeline. While they are defined as mandatory in the current YAML file, they allow an empty string as the value, which is not helpful. We need to refine their constraints without making them overly restrictive for external users. Specifically:

genome_assembly: should contain at least two digital numbers at the end (like hg19, GRCh37 ...)
file_type: should not be an empty string, should not start with a space, and should not contain a quotation