journal-remote: convert to the new option parser

journal-remote: convert to the new option parser

Replace the getopt_long()-based parser with the FOREACH_OPTION /
OPTION_* macros from src/shared/options.h, mirroring the recent
conversions of nspawn and vmspawn. Each option's metadata (long
name, short name, metavar and help text) now lives next to its
parsing logic, and the --help text is generated from those
definitions via option_parser_get_help_table() instead of being
hard-coded.

Positional file arguments are collected via
option_parser_get_args() rather than strv_skip(argv, optind).