Allow managing members in the project resource (#480)

* Extend resource and datasource

* Adapt acc test to work without members

* Extend acc test and adjust resource

* Generate docs

* Fix lint

* Fix unit test

* Uniformize description with datasource and extend unit test

* Improve role field description

* Update TF state before adding/removing members

* Remove unused function

* Move intermediate map top state to mapProjectFields

* Improve code

stackit/internal/core/core.go

@@ -18,6 +18,7 @@ type ProviderData struct {
 	ServiceAccountEmail             string
 	Region                          string
 	ArgusCustomEndpoint             string
+	AuthorizationCustomEndpoint     string
 	DnsCustomEndpoint               string
 	IaaSCustomEndpoint              string
 	LoadBalancerCustomEndpoint      string