Add support to non package_mode Poetry projects

[falkets]

From release 1.8.0 Poetry added the configuration 'package_mode', which allows users to use Poetry as a dependency management tool only, without the need to define a package in the project

Having the support to that parameter on 'poetry-plugin-bundle' would allow users to easily create fresh virtual environments in a given path with a single command.

Currently, trying to bundle a non 'package_mode' job leads to an error