Support running lium sync without `--version` option

[4n12i]

Unlike the original repo sync command, lium sync cannot be executed without specifying a version.

[4n12i]

Discussed offline with @hikalium :
There is a problem that if running repo sync without specifying the version, the build may not pass. Therefore, implement it to print a hint message instead of executing repo sync when executed without the --version option.
The hint message indicates the need for the version option and suggests possible versions.