Change OpenSea Testnet chain to Goerli

[nigimaxx]

The OpenSea Testnet API now uses the Goerli Testnet work (https://docs.opensea.io/reference/testnets-api-overview#:~:text=Ethereum%20Goerli%20test%20network)

This causes issues when trying to import a NFT on a testnet. Loading the metadata of the contract currently always fails.

Changing the RINKEBY_CHAIN_ID constant to a GOERLI_CHAIN_ID constant would probably solve this issue.

https://github.com/MetaMask/controllers/blob/main/src/constants.ts#L9

[desi]

This was handled by #1041