Add the data source for the project resource

[mipo256]

Currently, the terraform provider allows for the creation of the project resources, which is great.

The problem is that if I have to deploy a managed K8s cluster, I have to specify the project_id. That seems to be a no bid deal to provide a variable for that, but it is a error prone approach since variables are typed by humans.

On the other hand, we can not reference the project's id since we do not have a data source for that.

Importing the resource into the terraform configuration is an option but a clumsy one because I do not really want to declare and store those project resources that are huge BTW because of the quotas and etc. Just importing them as data sources would be a concise solution.