file publishing should report errors

At present, if you add a [[publish]] directive to the TOML, but something about it was wrong, we not only do not fail the job but we don't even report the problem. This happens in wollogong, in the basic variety code:

            /*
             * Resolve any publishing directives.  For now, we do not handle
             * publish rules that did not match any output from the actual job.
             * We also do not yet correctly handle a failure to publish, which
             * will require more nuance in reported errors from Dropshot and
             * Progenitor.  This feature is broadly still experimental.
             */
            for p in c.publish.iter() {
                if let Some(o) =
                    outputs.iter().find(|o| o.path == p.from_output)
                {
                    b.job_output_publish(
                        jid,
                        &o.id,
                        &buildomat_openapi::types::JobOutputPublish {
                            series: p.series.to_string(),
                            version: cs.head_sha.to_string(),
                            name: p.name.to_string(),
                        },
                    )
                    .await
                    .ok();
                }
            }

https://github.com/oxidecomputer/buildomat/blob/085e7685f3d3a6b99edbd7fb336533c84bf64fbe/github/server/src/variety/basic.rs#L420-L443

It is probably time to consider this less experimental:

• publish directives for files not produced as output artefacts should be reported and fail the job
• publish failures for otherwise present output artefacts should be also be reported and fail the job

Start in github/server/src/variety/basic.rs around the publishing loop at lines 420-443, and inspect how job_output_publish results and missing output artifacts are handled. Done means an unmatched publish directive reports an error and fails the job, and a failed publish for an existing artifact is also reported and fails the job.