Ignore Conway Genesis, except in SanchoNet

[sgillespie]

The Conway genesis file frequently changes in backwards-incompatible ways, causing errors like this:

cardano-db-sync: Error SNErrConwayConfig: Failed reading Conway genesis file "/configs/conway-genesis.json": "There was an error parsing the genesis file: /configs/conway-genesis.json Error: Error in $.poolVotingThresholds: parsing Cardano.Ledger.Conway.Core.PoolVotingThresholds(PoolVotingThresholds) failed, key \"pvtMotionNoConfidence\" not found"

There's no need to load the Conway genesis, unless we're in a network that's in Conway (currently only Sancho). For this reason, we should create a config parameter in the db-sync config, say "EnableConway", defaulting to false. This way, we'll only attempt to load the Conway genesis if necessary, which should address this issue for users of Mainnet, Preview, and so on.

[rdlrt]

Partly also discussed in #1665 , how will this help in future forks?

1. The config param only applicable on Conway? When we go to next era (if it has new genesis), we will have similar issue
2. Will be a stale leftover when we are on Conway across all networks?

Instead - Can this be generalized to something like EnableFutureGenesis ?

[sgillespie]

How will this help in future forks?

I don't think it will help directly.

Will be a stale leftover when we are on Conway across all networks?

There will be, and we'll need to clean it up as soon as we can.

Instead - Can this be generalized to something like EnableFutureGenesis ?

This is not a bad idea. @kderme thoughts?

[kderme]

EnableFutureGenesis seems like a good idea long term.
I believe node config had something similar at some point, but not sure why it was dropped