Fix missing proposer in proposal endpoint

The proposer is never returned in the /proposals/{id} endpoint. The code was commented out because the akash proposer endpoint is returning an error for proposals created during genesis. On top of that, the workaround of checking for only post-genesis proposals (id > 3) doesn't work for sandbox/testnet.

Failing akash endpoint: https://akash-api.polkachu.com/gov/proposals/1/proposer

We need to:

• Make sure proposer is returned for all proposal (pre or post-genesis)
• Make sure this works with sandbox/testnet so no hardcoded proposal ids

We could also consider removing the endpoint or proposer entirely in the if there is no need for it anymore.

Start in api/src/services/external/apiNodeService.ts at the commented-out proposer lookup and reproduce the failing Akash proposer endpoint for genesis, sandbox, and testnet proposals. Determine whether the proposer endpoint should be retained or removed; done means the proposal endpoint consistently returns a proposer across environments, or the proposer field and dependency are removed if no longer needed.