machinectl: convert to OPTION and VERB macros

machinectl: convert to OPTION and VERB macros

For the shell verb we want switches specified after the program name to
be passed to the program to execute, not processed by us. Mirror the
approach in 'userdbctl ssh-authorized-keys': start with
OPTION_PARSER_RETURN_POSITIONAL_ARGS, then lates switch to
STOP_AT_FIRST_NONOPTION for "shell" or NORMAL otherwise.

VERB declarations are placed directly above each function; functions
that dispatch multiple verb names get stacked VERB() declarations.
chainload_importctl() now takes the args strv instead of relying on the
global optind.

--help output is mostly the same.
--no-pager/--no-legend/--no-ask-password/-q/--quiet are now at the end.
bind-volume/unbind-volume are documented.

Fixes c9f461a8067996c6b0c3ac3bf6f9097aedbf4734.

Co-developed-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>