Switch L2 ledger to Conway

[ch1bo]

Why

While the Cardano node needs to be able to maintain support to all past eras (to verify the full chain), a Hydra head has a definite beginning and end of existence.

As maintainers of a hydra-node, we want to drop support for old eras to improve maintainability.

The next hard-fork event will be the fork into Conway era in Q1 or Q2 2024.

After #1177, we want to drop support for Babbage eventually.

What

• A new version of hydra-node which requires a Conway network is created.

• The hydra-node does detect and inform users when the network is still in Babbage era.

  • This may be just the same mechanism as described in #1177
  • Additional instructions or documentation to connect "later" when synchronized may be appropriate here.

• The layer 2 ledger does understand Conway transactions (i.e. this includes PlutusV3 scripts)

How

• [x] Preparing this already prior to the hard-fork
  • would allow us to push any problems we have upstream!
  • Early adopters can use plutusv3 and conway with hydra already before the hard-for
• [x] Change the Hydra protocol transactions to be Conway transactions.
  • As this is a breaking change already, we might want to switch to PlutusV3 as well here
  • Keep the "fixed" type Era alias, but just point it to ConwayEra