Add BSC integration

[leetdev]

Add support for BSC as per #335:

• Deployed contracts on both BSC Mainnet and Testnet and added addresses to README
• Added BSC HMT token contract (deployed by Multichain)
• Added subgraph deployment to GitHub graph deploy workflow (please note that humanprotocol/bsc subgraph needs to be created on thegraph hosted service)
• Added link to my GitHub profile in the network maintainers list

Additionally, improved the truffle deploy_contracts migration script to include deployment of the EscrowFactory contract.

[CLAassistant]

All committers have signed the CLA.

[Dzeranov]

@leetdev

1. Please add a proper description to this PR.
2. Add BSC contracts source code (like it was previously done for polygon contracts).

[leetdev]

@Dzeranov,

1. I've updated the PR description.
2. Do you mean to the network explorer? If so, then I've already done that, see:
   • EscrowFactory: 0x161228DaAB6F935548E2B98f6cedC9FF648C781d
   • KVStore: 0x8340412Ed68BcF53a7Da72BFFc1E2E74CfdE74D0

[Dzeranov]

@leetdev ,

No, I mean to this repo. As you can see we have a folder polygon_contracts in this repo. So we need a similar one for bsc.

[leetdev]

@Dzeranov I'm not sure what needs to go into that folder. Polygon I believe has its own underlying token contract for the Multichain bridge, but I saw no need to create one for BSC. The only contracts I deployed there were the Escrow Factory and the KV Store.

[Dzeranov]

@leetdev If we have a contract (in any chain) which source code is different from the one you can see in contracts folder, it should be represented in this repo for at least two reasons:

1. We need to review it.
2. It's inconvenient to check the source code in the explorer.

[leetdev]

@Dzeranov The HMT contract on BSC was deployed by Multichain as part of the bridge setup. Should I look for the source code for that and add it here?

[Dzeranov]

@leetdev Yes please.

[leetdev]

@Dzeranov I've added the token contract source code that was deployed by Multichain (verifiable at https://bscscan.com/address/0x0d501B743F22b641B8C8dfe00F1AAb881D57DDC7#code).

[eugenvoronov]

Hi @leetdev! Thank you for your work! We noticed that the contract is not upgradable, could you also do a proxy implementation, as is done for the polygon_contracts?

[leetdev]

@eugenvoronov, I'm not sure what exactly you want me to do. I explained, that the polygon bridge was set up in a different way - Multichain supports both bridging to an existing token (as is the case with Polygon) as well as creating a bridge without an underlying token contract. I was not in charge of setting up the bridge, all I did was suggest using Multichain. There are other HMT bridges that have been set up using the latter model, and I don't see any proxy contracts for those. Am I missing something?

[posix4e]

@leetdev i need to discuss this change with you can you reach out over discord?