[SPEC] Extend the Relayer Metrics system

[shekohex]

Overview

Right now the relayer metrics supports tracking for the gas_spent and total_fee_earned ...etc. But these are too generic, they are calculated over the whole networks and chains. Which is not the best data we shall provide.

Solution

Instead of having one total counter for the gas_spent and fees, we should have many of them in a map between the ResourceId and the Counter, so that we can query these data across different bridges or different networks ..etc.

We need these information for each Chain/Bridge:

1. Gas Spent.
2. Fees earned.
3. Account balance (as a counter that just have a single value).