Index SafeSetup event of Gnosis Safe 1.3.0 to retrieve initial owner

[adzialocha]

Tasks:

• Index SafeSetup event in subgraph to retreive initial owner for newly deployed 1.3.0 Safes. Related PR in Safe Contracts: Closes #233: Add setup event safe-global/safe-smart-account#279

Notes:

This will give us compatibility with all Gnosis Safes deployed from version 1.3.0 on. Note that original Safes (aka not our forked one) will still not be supported between versions 1.0.0 - 1.3.0. This issue tries to tackle this: #59

[llunaCreixent]

Context:

In order to index the owner of a Safe when it's deployed, we created a fork of the 5afe/safe-contracts v 1.1.1 and introduced the emission of a AddedOwner event in the setupOwners() function of the OwnerManager contract.
In the version 1.3.0 of the 5afe/safe-contracts, the aforementioned event doesn't exist (see https://github.com/safe-global/safe-contracts/blob/main/contracts/base/OwnerManager.sol#L22), but instead an event with the same purpose has been added in the etup()funcion of theGnosisSafe` contract (see SafeSetup event in https://github.com/safe-global/safe-contracts/blob/main/contracts/GnosisSafe.sol#L96).

Since we want the subgraph to index the data coming from both Safe versions we need to add a handler for the SafeSetup event.

[llunaCreixent]

The only drawback with this approach is that we are registering all the Safes, and not only the ones that signed up to the Hub.
We should re consider if we want to index only the Safes that are signed up to the Hub. We could do it by checking if the Safe is signed up every time we create a new Safe entry in the subgraph database.

[llunaCreixent]

Created a new issue: #85