Add ability to toggle dependency 'develop'

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Feature Request

Path-dependencies in Poetry can be optionally marked as 'develop' = True. However, there’s no way to mark it as such via the poetry add command.

It would be nice to set the 'develop' = True when adding a path. For example:

poetry add ./my-package/ --develop

Or

poetry add ./my-package/ --editable

I think I can implement this myself if the core devs consider this feature to be beneficial.

[abn]

I think this can happen independent of #3004. If this happens first, we just update the key it operates on when #3004 lands.

[finswimmer]

This is now possible in the current preview release 1.2.0a2 by:

-e, --editable           Add vcs/path dependencies as editable.