Support importing for env0_user_project_assignment

[ankon]

Is your feature request related to a problem? Please describe.

I created a API key manually and assigned a few project roles to it. Later I wanted to import that key through the Terraform provider, but then saw that it actually doesn't support import.

Describe the solution you'd like

It should be possible to import these resources.

Describe alternatives you've considered

1. Remove the assignments from the API key, and create the resources --> Doesn't work, because one seemingly cannot edit the API key in the UI. I still need to check whether I can manually remove them from all projects ...

[ankon]

I still need to check whether I can manually remove them from all projects ...

Yes, this worked: Remove the existing assignments, then add the new ones I wanted to import.

Does point to a UI issue though: I create permissions when setting up API keys in that dialog, but later on nothing on the API key overview hints at this API key is now just a normal user and the permissions it has are distributed all over the projects.