6749: Add local git repository source option (`--local_git`) to plugin installation r=indirect a=indirect

Reopening #6338 to close #5446.

Co-authored-by: Saverio Miroddi <saverio.pub2@gmail.com>

If the lock file has the same gems for different platforms, the
suggestion includes all those gems.

For example, using the Rails's lock file(https://github.com/rails/rails/blob/4a51cbba58435bbba65ca50670bd6ae4887942bd/Gemfile.lock),
it shows like this:

```
$ bundle update mai
Could not find gem 'mai'.
Did you mean ffi, ffi, ffi, ffi, mail, ast, jwt, que or wdm?
```

Since it is unnecessary to include the same gem, removed duplicate gems.