misc/coverage: Improve display of origin counters in production/staging
If the global counter for an origin type is equal to zero, do not display the bootstrap card for that origin type.
If a visit type counter for an origin type is equal to zero, do not display it in the counters table for that origin type.
It enables to not take into account origins that have been listed but not loaded without having to hardcode that information in coverage widget implementation.
Also use origins_enabled field from scheduler metrics instead of origins_known one to compute the number of loaded origins per visit type.
Related to swh-docs#3117
Below are the results obtained after applying that diff and a couple of other ones adding new origin types (maven, phabricator).
Migrated from D7819 (view on Phabricator)