permit submission of creatives that fail validation

[tackley]

Currently, some self-serve advertisers may experience a 403 error or unexpected failures when validating their URLs due to DDoS protection or technical errors. This issue prevents the campaign from progressing beyond the creative setup stage, and may result in the loss of the advertiser.

Proposed Solution:
If URL validation fails with a 403 error or unexpected failure, the submission will still pass checks and advance to the ad ops review queue. Ad ops will manually review and validate the URL to ensure the creatives do not include any redirects, and the failures are false failures.

Originally posted by @StephenBass in https://github.com/brave/ads-serve/discussions/3945

[diracdeltas]

Ideally this would just be solved by making the validation service more robust. If it has to fall back to a human check, someone needs to make sure the human process is updated whenever the automated checks are updated.