The `error_expected` custom attribute used to contain
both the class name and the error message. This had
the following issues:
* Combining data in the same custom attribute limits
the ability to query.
* The additional error class and message data is only
needed for ignored errors, since this data isn't
available elsewhere.
The following changes were made:
* `error_expected` will always have the value True
if present.
* `error_ignored` no longer exists.
* `error_ignored_class` will contain the error module
and class for ignored errors.
* `error_ignored_message` will contain the error message
for ignored errors.
ARCHBOM-1708
Adds logging and monitoring capabilities for expected
errors. See the ADR and how-to documentation for
details of how to configure and use the EXPECTED_ERRORS
setting and new monitoring and logging.
ARCHBOM-1708
Co-authored-by: Tim McCormack <tmccormack@edx.org>