Make --fee mandatory in transaction build-raw

[carbolymer]

Changelog

- description: |
    Make `--fee` mandatory in `transaction build-raw`. Remove `TxCmdTxFeeValidationError` type.
# 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

Seems that fees should be mandatory for eras >= Shelley, but the CLI interface wasn't saying so and was defaulting to 0.

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

[carbolymer]

I'm unsure about this bit. I guess it makes sense to say in the function signature, that the fee is required and let users specify 0 if needed.

[carbolymer]

As far as I understand, in Byron the fee is still optional?