rename main CLI command from "swh fuse" to "swh fs"
rationale:
- it is consistent with SwhFS which we are now using in doc
- FUSE is an implementation detail, which has no place in user-facing names
- it is consistent with other FUSE-based FS (sshfs, RepoFS, etc.)
Test Plan
tox
Migrated from D4314 (view on Phabricator)