Validator error responses could be better reflected in the testbed output

If a validator produces an error response it might be better to include more information in the test failure output produced by the testbed. For example, if an invalid XML file is fed into a validator, the testbed will report:

*** ApiError code 400 in adfs/bad_adfs_idp_sso_lacks_binding on v09x's default validator

From that, It's hard to determine the cause of the error, but the validator's response is detailed in comparison.

{
  "exception": "uk.org.iay.md.validator.api.ApiException",
  "path": "/validators/default/validate",
  "cause": "org.xml.sax.SAXParseException; lineNumber: 2; columnNumber: 6; The processing instruction target matching \"[xX][mM][lL]\" is not allowed.",
  "error": "Bad Request",
  "message": "XMLParserException: Invalid XML",
  "status": 400,
  "timestamp": "2024-02-27T10:43:12.361884339Z"
}

Some of that could be reflected in the testbed output.

ukf / ukf-testbed

Validator error responses could be better reflected in the testbed output #81