chore(prometheus.blackbox): update to 0.28.0

[xanderio]

Brief description of Pull Request

Update vendored blackbox exporter to 0.28.0, this enables to uses of fail_if_body_json_not_matches_cel and fail_if_body_json_matches_cel

Pull Request Details

Issue(s) fixed by this Pull Request

Fixes #4083

Notes to the Reviewer

PR Checklist

• Documentation added
• Tests updated
• Config converters updated

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[kalleep]

Thanks for taking this on. It's probably now enough to just bump the go dependency but we probably need to map new config for the exporter to alloy arguments so they can be configured, I see you mention fail_if_body_json_not_matches_cel and fail_if_body_json_matches_cel