Merge the two storages and give users the ability to write their own database drivers

[luckyycode]

CatraProto currently supports the only one session serializer of type FileSerializer Application is hosted in Kubernetes container and it's not comfortable to use FileSerializer because it requires app to have a local path to store session data

My request is to document IAsyncSessionSerializer interface and let end-user to choose what type of storage one would like to use. Currently it's sqlite, but maybe CatraProto should have a separate interface for session storage to abstract away from sqlite and use custom storage together with custom IAsyncSessionSerializer implementations