refactor: snapshot listing query type

[Abhinandan-Purkait]

TypeDef:

 message Query {
        optional bool invalid = 1; // Filter based on invalid if some.
        optional bool discarded = 2; // Filter based on discarded if some.
    }

Worflow:

• If Query.invalid or Query.discarded is Some(val), compare the SnapshotInfo with the val followed by && operation.
• If Query.invalid or Query.discarded is None, don't include the field in compare of SnapshotInfo.

[tiagolobocastro]

Ah sorry I shouldn't have merged this yet as io-engine PR is not yet ready..