install: support -i flag for specifying SSH private key

pkgs/clan-cli/clan_cli/machines/install.py

@@ -36,6 +36,7 @@ class InstallOptions:
     nix_options: list[str] = field(default_factory=list)
     update_hardware_config: HardwareConfig = HardwareConfig.NONE
     password: str | None = None
+    identity_file: Path | None = None
 
 
 @API.register
@@ -97,6 +98,9 @@ def install_machine(opts: InstallOptions) -> None:
                 "IdentitiesOnly=yes",
             ]
 
+        if opts.identity_file:
+            cmd += ["-i", str(opts.identity_file)]
+
         if not machine.can_build_locally or opts.build_on_remote:
             machine.info(
                 f"Target machine has architecture {machine.system} which cannot be built locally or with the configured remote builders. Building on target machine"
@@ -170,6 +174,7 @@ def install_command(args: argparse.Namespace) -> None:
                 build_on_remote=args.build_on_remote,
                 update_hardware_config=HardwareConfig(args.update_hardware_config),
                 password=password,
+                identity_file=args.identity_file,
             ),
         )
     except KeyboardInterrupt:
@@ -233,10 +238,17 @@ def register_install_parser(parser: argparse.ArgumentParser) -> None:
         help="ssh address to install to in the form of user@host:2222",
     )
     add_dynamic_completer(target_host_parser, complete_target_host)
-    parser.add_argument(
+    authentication_group = parser.add_mutually_exclusive_group()
+    authentication_group.add_argument(
         "--password",
         help="specify the password for the ssh connection (generated by starting the clan installer)",
     )
+    authentication_group.add_argument(
+        "-i",
+        dest="identity_file",
+        type=Path,
+        help="specify which SSH private key file to use",
+    )
     group.add_argument(
         "-P",
         "--png",