refactor: changed gRPC web route to consensus_states/{client_id}/heights

[crodriguezvega]

Description

While I was backporting #1336 I realized that the gRPC web route for consensus_state/heights/{client_id} was not aligning with the URL format that we want to have, so I am changing it to consensus_state/{client_id}/heights. I have already made the same change in the branches to backport the PR that are currently open: #1505 #1506 #1507

closes: #XXXX

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[damiannolan]

LGTM!