clair3 vcf does not respect VCFv4.2 standard

[ChR-1610]

VCF header states:

##clair3_version=1.0.8
(...)
##FORMAT=<ID=AF,Number=1,Type=Float,Description="Observed allele frequency in reads, for each ALT allele, in the same order as listed, or the REF allele for a RefCall">

VCF header should state

##FORMAT=<ID=AF,Number=.,Type=Float,Description="Observed allele frequency in reads, for each ALT allele, in the same order as listed, or the REF allele for a RefCall">

Reason

Since more than one ALT can occur, the AF Format should state <ID=AF,Number=., (etc)>. In other words Number=. (dot) is correct while Number=1 only allows for one ALT and is therefore wrong.

[ChR-1610]

This version of clair3 is in use in Oxford Nanopore EPI2ME software package, where it was discovered.