Feature request description/rationale

The existing code throws a MissingChainError error when edge validation fails when no edge operator is specified. Due to the default edge operation being and the I2I operator when the op is None then the failure is currently confusing.

What would be useful for the user of KERIpy is to see an error specific to edge operator validation failure like an EdgeOperatorValidationError or something like that and it would also be useful to show the occurrence of this error in a log message. Showing such errors in the logs would help avoid duplicate issues like #775.