Web API URL setting in configuration file ignored

$ cat ~/.config/swh/global.yml
swh:
  fuse:
    web-api:
      url: "https://archive.internal.softwareheritage.org/api/1/"

according to the config doc this should work, but it doesn't, all my requests are nonetheless directed to the public Web API (I'm sure of this due to #2709 (closed)), where I've quickly hit the rate-limit.

Relatedly, it would be nice to log at start time the configuration settings that have //actually// been loaded, it will make debugging this kind of problems easier for end users.

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Migrated from T2711 (view on Phabricator)