reset password fails if credentials record does not already exist

A POST request to bl-users/password-reset/reset fails with a 500 if the corresponding record from authn/credentials is not already present.

The failure comes from mod-login's POST /authn/password/repeatable, invoked via the default mod-password-validator rule here:
https://github.com/folio-org/mod-password-validator/blob/f8864c413dbac105d49b7b9f3b377d4dbaab64bb/ramls/defaultRules/defaultRules.json#L101

If a credential record is not found the passwordStorageServiceImpl fails the promise/future returned by getCredsById(...)
https://github.com/folio-org/mod-login/blob/c3c6263f5520319f1208d47e04e70ca6bd39f8f4/src/main/java/org/folio/services/impl/PasswordStorageServiceImpl.java#L435 causing a 500 Internal Server Error to be returned w/o any context.

The error handling should be adjusted so that when a credentials record doesn't exist POST /authn/password/repeatable returns a response indicating that the password is not a repeat.