More sanity checks on Managed variants

[dnil]

Is your feature request related to a problem in the current program to new available techology or software? Please describe and add links/citations if appropriate.
Managed variants currently allows relatively free text entries. While a simple solution not to have to have a filter with full knowledge of what a valid variant is, it is potentially complicated for downstream usage, both in matching and export. A power user can use this to her advantage, but may sometimes not be aware of the way certain variants are stored, and will typically not have an example variant to copy or test with - then it could be flagged causative.

Describe the solution you'd like
Add more checks on managed variants input format, e.g. subcategory aware controlled vocabulary on ref and alt.

See e.g. #4969...

[dnil]

Without more filters on the free text fields, this lends self to situations where the variant cannot be properly edited.