Fetches a specific block from the validator, specified by id.
        Request:
            path:
                - block_id: The 128-character id of the block to be fetched

        Response:
            data: A JSON object with the data from the fully expanded Block
            link: The link to this exact query

async def fetch_block(self, request):
        """Fetches a specific block from the validator, specified by id.
        Request:
            path:
                - block_id: The 128-character id of the block to be fetched

        Response:
            data: A JSON object with the data from the fully expanded Block
            link: The link to this exact query
        """
        error_traps = [error_handlers.BlockNotFoundTrap]

        block_id = request.match_info.get('block_id', '')
        self._validate_id(block_id)

        response = await self._query_validator(
            Message.CLIENT_BLOCK_GET_BY_ID_REQUEST,
            client_block_pb2.ClientBlockGetResponse,
            client_block_pb2.ClientBlockGetByIdRequest(block_id=block_id),
            error_traps)

        return self._wrap_response(
            request,
            data=self._expand_block(response['block']),
            metadata=self._get_metadata(request, response))