Add --conway-era flag

[newhoggy]

Description

Add --conway-era flag.

There is still an unresolved error that will be resolved separately:

cardano-cli transaction build --conway-era --testnet-magic 42 --tx-in 'bf1e7a5edbd698b7b19f88a2761161247c31d0a0a989394f6e9ff51b450d72b2#0' --tx-out 'addr_test1vzvgd5ezqhwde7qjl428kkvaqnlfx3hvd27kcn4ahxc2zssc7d7he+300000000' --change-address addr_test1vqyug3rskwm2nur6zsdnwqznrs4gdqlp275pqqzrtuuxc0cmr6wc0 --out-file tx.raw

cardano-cli: Prelude.undefined
CallStack (from HasCallStack):
  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
  undefined, called at src/Cardano/Ledger/Conway/TxBody.hs:311:18 in crdn-ldgr-cnwy-1.2.0.0-d7c84ea9:Cardano.Ledger.Conway.TxBody

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests
    See Runnings tests for more details
• Any changes are noted in the CHANGELOG.md for affected package
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• Self-reviewed the diff

Note on CI

If your PR is from a fork, the necessary CI jobs won't trigger automatically for security reasons.
You will need to get someone with write privileges. Please contact IOG node developers to do this
for you.