sftp: add support for configured IdentityFile

src/borgstore/backends/sftp.py

@@ -50,6 +50,7 @@ def _connect(self):
             hostname=scd.get("hostname", self.hostname),
             username=scd.get("user", self.username),
             port=scd.as_int("port") if "port" in scd else self.port,
+            key_filename=scd.get("identityfile", None),
             allow_agent=True,
         )
         self.client = ssh.open_sftp()