Refactor seqvar query query schema and use protobuf for input

[holtgrewe]

Is your feature request related to a problem? Please describe.
We currently use JSON serde-serialized data structures for the query schema in seqvars query. This requires us to replicate the schema data structure on the Python side. Further, there is a 1:1 relation between the input and the internal data structures.

Describe the solution you'd like

• Provide a protobuf schema file for the query definition data structures.
• Use prost to obtain Rust data structures from them.
• Read such protobuf from JSON using pbjson.
• Convert them to the internal data structures.
• Run the program as currently.

Describe alternatives you've considered
N/A

Additional context
The data structures for representing queries are defined in seqvars/query/schema.rs. The seqvars query command is currently not called from the Python server.