fix: #96 add condition to verify if network is testnet

[Sotatek-HuyLe3a]

Root cause: misssing condition to verify a network is testnet -> reward account hex calculation is wrong when certificate is pool registraion. (BlockAggregatorServiceImpl.java)

                // Reward account
                // Workaround for bug https://github.com/input-output-hk/cardano-db-sync/issues/546
                String rewardAccountHex = poolRegistration.getPoolParams().getRewardAccount();
                byte[] rewardAccountBytes = HexUtil.decodeHexString(rewardAccountHex);
                int networkId = Constant.isTestnet(network) ? 0 : 1;
                byte header = rewardAccountBytes[0];
                if (((header & 0xff) & networkId) == 0) {
                    rewardAccountBytes[0] = (byte) ((header & ~1) | networkId);
                }
                blockDataService.saveFirstAppearedTxHashForStakeAddress(
                        HexUtil.encodeHexString(rewardAccountBytes), txHash);

[satran004]

@Sotatek-HuyLe3a I think we can change this logic to networkMagic != MAINNET, then it's Testnet

[Sotatek-HuyLe3a]

I just updated @satran004