[services][blob] Define database error types

Summary:
Defined error enums and structures to be used in DatabaseClient.
This code is very similar to the identity and backup service approach.

Depends on D5855

Test Plan: Cargo check doesn't complain.

Reviewers: varun, jon, tomek, michal

Reviewed By: varun, jon, tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D5856