feat(cat-voices): proposal viewer collaborators

[dt-iohk]

Description

Adds collaborators to the proposal viewer page.

Related Issue(s)

Closes #3686

Screenshots

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• I have added tests that prove my fix is effective or that my feature works
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[github-actions]

📚 Docs Preview

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

https://docs.dev.projectcatalyst.io/voices/feat/proposal-viewer-collaborators-3686

[damian-molinski]

LGTM