Draft the new, definite textEnvelopeType for Tx

[ch1bo]

All transactions are now serialized and deserialized as 'Witnessed' transactions using the Ledger binary format.

Changelog

- description: |
    **BREAKING** Text envelope type of `Tx era` is now always using the new `Witnessed Tx` prefix.
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

Draft for the transaction envelope type that a cardano-api transaction should have going forward. Before, only serialiseTxLedgerCddl would produce the correctly parseable Witnessed Tx ConwayEra for example. However, that function is deprecated and we should fix the serialiseToTextEnvelope invocation for Tx era directly.

How to trust this PR

There are probably several things missing and this is just a draft for how I, as a user, would want the cardano-api/-cli to operate (using a single Witnessed Tx <era> type).

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff