Move BCFTOOLS convert to vcf extract

[LouisLeNezet]

Description of feature

Generate and use only one posfile format.

### Tasks

[LouisLeNezet]

Future improvements should include creating a posfile that can be used by all tools with the least amount of transformation steps.
We could only convert once the panel then use the generate posfile for all imputation subworkflow and in each of them convert to the right format.