feat: add `--offline` flag in `create` command

[yeikel16]

Description In some cases I do not have the network available to create a project with the client, it needs to download several dependencies. It would be very helpful to make use of the caching system available in the environment variable PUB_CACHE by using the --offline flag when creating both a project like packages or some plugin.

I would like to work on this feature if possible.