Detect a transaction when created

[gipsh]

Currently we only detect a transaction when the first observation reach fly as we tap into the gossip network.
There are some cases with chains with longer finally times (ie eth and polygon) where a tx is created but we wouldnt see an observation
many minutes after the event.
This of course depends of the consistency level defined on the VAA but for token bridge its always finality .

So what we need is a way to represent better the life cycle of a vaa:

• tx created (waiting for finality or consistency level defined)
• tx finalized (observation started to arrive)
• signed vaa emitted (obs count > 15)
• vaa relayed
• vaa redemeed

To achieve the first step is not enough to tap into gossip network, we will need to watch for node logs and detect the event of the tx creation or the publish message emitted by the contract.

Implementation

First step is to create a stand alone service.
This service will connect to each node (for now only eth and polygon) and
wait for messages from the core layer contract.
Once a message is detected store it an wait for finality.

Provide an API to check if a TX is pending / finalized.

Take a look at watcher impl for inspiration here

(discuss implementation details with the team)

[agodnic]

Breakdown into actionable tasks:

• 1. [event-watcher] Create service boilerplate #378
• 2. [event-watcher] Create a watcher for Ethereum #379
• 3. [event-watcher,api] Create an endpoint to query tx status #380
• 4. [event-watcher] Create a connector for Polygon #381
• Add finality logic to the Ethereum connector (currently, we're not whether sure this is needed)
  • Probably need to subscribe to block events. 1 2 3