swh-docs : List out public URLs of web applications served by SWH instances

Some examples could be :

• https://deposit.staging.swh.network
• https://webapp.staging.swh.network
• https://grafana.softwareheritage.org
• https://sentry.softwareheritage.org

IMO, these can be added at the end of https://docs.softwareheritage.org/devel/issue-debugging-monitoring.html

---

Migrated from T3114 (view on Phabricator)