cli: use "_ALL_PROVIDERS" as for provider options (#4308)

Signed-off-by: Robert P. J. Day <[email protected]>
Co-authored-by: Callahan <[email protected]>

snapcraft_legacy/cli/_options.py

@@ -191,7 +191,7 @@ def __repr__(self):
         is_flag=True,
         help="Enable plugins that are experimental and not considered stable.",
         envvar="SNAPCRAFT_ENABLE_EXPERIMENTAL_PLUGINS",
-        supported_providers=["host", "lxd", "managed-host", "multipass"],
+        supported_providers=_ALL_PROVIDERS,
     ),
     dict(
         param_decls=["--enable-experimental-target-arch"],