Create unit tests for WebLedgerConfiguration validation

[mattcollier]

Currently, there are no unit tests for this:
https://github.com/veres-one/veres-one-validator/blob/cdd493cd19f740c0e28a2556179228b6b71759f2/test/mocha/12-validate-ledger-configuration.js#L6-L11