Add block height to the matches

[paluh]

Thanks for building such a nice and lean indexer!

What is your idea? Describe it in simple words. Provide a use case.

I want to add block_no information to the returned checkpoints and match properties (created_at and spent_at). This will not be part of any other point related API (so the point encoding would stay the same).

Why is it a good idea?

The depth of a block is formally associated with maturity of that block and probability of its rollback. On paper we have a particular depth value per chain which makes a given block fully settled.
In our case (the cardano-lightning/konduit server) we want to use the depth as an indicator for the tx maturity.

What is the current alternative and why is it not good enough?

We could estimate maturity through the slot number which is already present on the Kupo API level. In such a case we are forced to do a hand wavy explanation why we use it instead of a proper depth and explain that it is due to our upstream dependency - Kupo :-P

I have a draft PR which presents most of the required changes (PostgreSQL and Ogmios are still not tested yet): #212