refactor: make command accessible in option parser

[qweeah]

Currently options are parsed without any argument

oras/cmd/oras/internal/option/parser.go

Lines 22 to 25 in e8da6e5

	// FlagParser parses flags in an option.
	type FlagParser interface {
	Parse() error
	}

All option parser implementations are called in command.PreRunE, where command is actually accessible. Should pass the command to parser to facilitate cmd-specific parsing, e.g. processing the flag set.

[qweeah]

@wangxiaoxuan273 Can you resolve this first since it will simplify change in #1294