Send WARC import errors to Sentry

[Mr0grog]

When we have WARC import errors, we should send them to Sentry so we have better telemetry and metrics about what is failing. For example, this run: https://github.com/edgi-govdata-archiving/web-monitoring-crawler/actions/runs/18421870440/job/52497363504

No WARC records for seed: "https://marine.usgs.gov/coastalchangehazardsportal/"

Most of the work for this will be over in warc_import.py in the -processing repo, but we also need to set the SENTRY_DSN env var/secret here.