Omit errors from analytics when error_details available

[aduth]

🛠 Summary of changes

Updates FormResponse to assign errors to nil when error_details is available, thereby resulting in them being omitted from analytics logs.

As with #11799, this serves to reduce the size (and cost) of our logging payloads. As discussed with the team previously and as outlined in the SBAR document "IdP logging approach for error details", the current usage of errors is not valuable for log querying, and error_details should be preferred.

The changes here leave FormResponse is a somewhat fragmented state, but it does so intentionally to lessen the amount of changes.

Future pull requests will:

• Remove the serialize_error_details_only option altogether (make baseline behavior)
• Avoid assigning errors altogether, as opposed to assigning as nil
• Consider removing existing use of FormResponse with non-ActiveRecord::Errors errors type

📜 Testing Plan

Verify build passes.

Validate using make watch_events that event logs which would previously include errors no longer include the property, but still include equivalent error_details.

[aduth]

Noting that this is a change in behavior, though the previous implementation would log error_details with string keys derived from the user-facing string, which would make querying much more difficult. As best I can tell, we don't have any existing dashboards or alarms which relied on the previous format.

Before:

error_details: { InvalidStateError: { :" Please try again or choose another authentication method" => true } }

After:

error_details: { InvalidStateError: { invalid: true } }

[aduth]

Granting that this is still not a consistent format even after the changes, since keys of error_details should refer to the specific problematic field, not the error itself. This page is a bit unique in how it logs errors, but a better format might be something like...

error_details: { client_data_json: { invalid_state: true } }

client_data_json referring to one of the fields expected to be populated in the client-side form.

[zachmargolis]

LGTM, this seems like a good change to make sure to communicate widely internally just in case people had been consuming these errors fields instead of error_details