feat: add function to obtain eth bridge contracts

[TucksonDev]

First attempt to add these functions (tested on local with several generated networks).

Some notes:

• I've added the functions to the EthBridger and ERC20Bridger. Please let me know if you think they'd make more sense somewhere else
• I've created a new interface for the return value of the ERC20Bridger.getGatewayInformation() . That interface looks similar to TokenBridge from dataEntities/network.ts, but as I've added two new fields (l1Gateway and l2Gateway) I didn't want to touch too much the one in the network file.
• In that interface, l1Gateway and l2Gateway correspond to the information of the gateway passed as parameter, which could be a custom gateway. Not sure about the naming, but please let me know of any good ideas you might have.
• The logic of the functions should be simple enough, but I might have missed a shortcut somewhere. Please, let me know if that's the case.
• I've also fixed one logged variable in deployBridge.ts

[gzeoneth]

so I think the only thing you might want to add here is getL1CounterpartGateway and getL2CounterpartGateway. Also note that counterpartGateway is also not part of the token gateway interface, and you should validate the data the gateway return against the other side.

[TucksonDev]

Changed logic so only the EthBridge information is retrieved from now.
Moved it to the dataEntities/networks file as having it in the EthBridger file requires an L2Network to be set.

[spsjvc]

I'd move this test to integration tests since we're actually hitting the network and we're not mocking anything

[TucksonDev]

Test moved

[gzeoneth]

LGTM