Show proposal github links as bisq.network redirects

[devinbileck]

Now that URL validation for proposal links has been added (see #2705), the UI should show links for previous proposals that have a github link (e.g. from cycle 1) as the bisq.network redirects.

This is not a major issue for the time being since the github links are still valid. But they could potentially become dead links if we later relocate our proposals elsewhere and would be an issue if someone wants to view proposals from cycle 1 and attempts to follow the link to the proposal.

[stale]

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[stale]

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