CLI: "wasmer deploy" does not allow specifying a particular app.yaml anymore

[theduke]

In the recent refactors, "wasmer deploy" has lost the option to specify the path
to a speciic app.yaml.

Not having that option is annoying when you have multiple app.yamls for one package,
since it requires creating a separate sub-directory for each app...

[xdoardo]

The --dir flag allows to pass a path to the app.yaml file.
We either:

1. Change --dir to --path (breaking)
2. Leave --dir as it is and add --path

[theduke]

Option 2 sounds good to me.