Add option to allow adding alias even if there's already a binary in path with that name

Often we want to still add the alias even if it shadows an existing binary. While the check makes a ton of sense, having the option to skip it with a `--force` flag of some kind would be really useful.

Locate the command that adds aliases and read the existing check for a binary with the same name in PATH. Trace how command-line options are defined, then verify that the force option permits the alias and that the existing collision behavior remains unchanged.

索引モデルが issue の本文から書いたものです。