refactor: load Ethereum network based on Product.chain

[kare]

[linear[bot]]

BACK-204 Data Union: use Product.chain to load right network

When sanity checking Data Union admin's contract address use Product.chain to load the correct network. See EthereumService.fetchDataUnionAdminsEthereumAddress(String)

[github-actions[bot]]

This pull request is stale because it has been open 60 days with no activity. Remove no-pr-activity label or comment or this will be closed in 7 days

[hpihkala]

The DU join features in the core-api are now obsolete due to moving to the new join server, closing this