misc/coverage: Display counters for bzr/cvs visit types conditionally

When loading task types are available for these visit types in the swh deployment environment (currently staging and docker), display the associated counters in the coverage widget.

Related to swh-loader-bzr#3945 (closed)

Related to swh-loader-cvs#3835 (closed)

---

Migrated from D7221 (view on Phabricator)