`catalyst-contest` crate with `Contest Ballot` decoding

[Mr-Leshiy]

Summary

• Create a new catalyst-contest crate.
• This new crate will cover new Catalyst voting (contest) functionality.
• As a first step, implement ContentBallot document payload decoding according to the cddl spec (see link: https://docs.dev.projectcatalyst.io/libs/main/architecture/08_concepts/signed_doc/docs/contest_ballot).

Description

Implement the decoding for the ContentBallot (represented by contest-ballot-payload in CDDL) document payload using the minicbor crate.