Better error classification in `clients/feeder`

[ashu26jha]

Problem

Currently, if we try to fetch the block (lets say 1,000,000) from the feeder we get 400 Bad Request which is a generic error. Meanwhile the feeder gateway shows:

{"code": "StarknetErrorCode.BLOCK_NOT_FOUND", "message": "Block number 1000000 was not found."}

We want the error message to reflect the response.

Advantages

1. This will help in debugging.
2. This will be needed to improve reorg handling