Add ability to easily identify homozygous variants on the Variant Lookup page

[lynnpais]

Is your feature request related to a problem? Please describe.
For variants that have a relatively high AC in seqr, it's hard to go through all and effectively identify cases where it's homozygous.

Describe the solution you'd like
On the Variant Lookup page, add the ability a filter or sort - whatever is easiest to bring the homozygous cases to the top.

Describe alternatives you've considered
NA

Additional context
Anne & Lynn request

[hanars]

Thinking about this more I think it makes sense to do this in the backend, which would be much easier to do once the hail backend is gone. Can this wait?

[lynnpais]

Sure, if that is easier!

[lynnpais]

As discussed today, it makes most sense to add a filter.

In addition to filtering by het/homs, we'd also like the ability to filter cases where the variant is present in at least one affected individual.