DataTables - refactor after new feature to get queryset, not just values arrives

Do once James' new code hits master.

In datatables, we sometimes have to pull out objects, which means double (and row-by-row) queries. Eg:

```
@staticmethod
def render_allele(data: CellData):
if value := data.value:
allele = Allele.objects.get(pk=value)

```

I thought this happened a few times, but have only found 2:

ImportedAlleleInfoColumns.render_allele
VariantTagDetailColumns.can_write

Probably worth an audit looking for these, could speed things up a bit