Allow creation of top-level projects

[eleftherias]

Currently, we allow the creation of sub-projects, projects that are children of another project.
This issue tracks creating top-level projects, projects without a parent project.

We can repurpose the existing minder project create command.
We should deprecate the existing --project flag and introduce a new --parent flag to make it explicit that the new project will be a sub-project.
If no --parent flag is provided, then we should assume that it is a top-level project.