feat(docs): Contest Ballot payload improvement

[Mr-Leshiy]

Description

A slight improvement of the Contest Ballot document cddl definition, with minor fixes/updates of document definitions.

Related Issue(s)

Part of #634

Description of Changes

• Changed document_ref to uint for the Contest Ballot payload CDDL definition.
• Added missing ref metadata field definition for the Contest Ballot.
• Updated definition of the collaborators and document_refs types.

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

📚 Docs Preview

The docs for this PR can be previewed at the following URL:

https://docs.dev.projectcatalyst.io/libs/feat/contest-ballot-payload-update

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 585/585}$ | ${\color{red}Fail: 0/585}$ |