Add event indexer

[rcatalan98]

In order to provide a good and responsive front end we need to index events from the smart contract and stream the data. There are a couple of options to choose from, right now Apibara seems to be the best option.

The project should include a backend that allows for the stream of relevant data to a frontend. In particular, there needs to be an indexer for the events emitted by our two core smart contracts (Pool and Factory).