[FEATURE] - Add haddocks for cardano-testnet

[carbolymer]

Describe the feature you'd like
Currently haddocks on https://cardano-node.cardano.intersectmbo.org/ for cardano-testnet are broken. We should deliver API documentation for end users.

Additional context / screenshots
The current way of generating haddocks in cardano-api seems to be robust enough. We can try to use this for cardano-testnet as well: https://github.com/IntersectMBO/cardano-api/blob/master/.github/workflows/github-page.yml