Add blockchain stats endpoints

[rafaelcr]

We'd like to start exposing new endpoints that return statistics about the current state of the blockchain for different topics, included under a new router (e.g. /extended/v1/stats/...).

This issue tracks a list of sub-issues, one per endpoint:

• Endpoint(s) showing asset account distribution #1066
• feat: endpoint that exposes mempool size divided by tx status #982
• Add endpoint to return total deployed contracts

[rafaelcr]

This could also be a microservice

[andresgalante]

@rafaelcr are there any updates for this issue?

[rafaelcr]

@andresgalante after we opened this issue we were thinking this was going to become its own microservice given that taking these stats would add unnecessary complexity to the current API.

I think we should sync and come up with a reasonable timeline in which to do this, especially if you feel these are going to become important for the explorer to have so we can have them ready ASAP