Remove any leading slashes when parsing the backend from an IMAS URI

Fixes IMAS-5560, where an URI of the form `imas://host:port/uda?....` would log
`WARNING Backend /uda is unknown to IMASPy`

Author: maarten-ic

imaspy/backends/imas_core/db_entry_al.py

@@ -136,7 +136,7 @@ def from_pulse_run(
     @classmethod
     def _from_uri(cls, uri: str, mode: int, factory: IDSFactory) -> "ALDBEntryImpl":
         """Helper method to actually open/create the dataentry."""
-        backend = urlparse(uri).path.lower()
+        backend = urlparse(uri).path.lower().lstrip("/")
         cls._setup_backend(backend, mode, factory)
 
         status, ctx = ll_interface.begin_dataentry_action(uri, mode)