add scope datasource, tests, and docs (#474)

* add scope datasource, tests, and docs

* add details on the global scope to docs

examples/data-sources/scope/data-source.tf

@@ -0,0 +1,10 @@
+# Retrieve the ID of a Boundary project
+data "boundary_scope" "org" {
+  name     = "SecOps"
+  parent_scope_id = "global"
+}
+
+data "boundary_scope" "project" {
+  name     = "2111"
+  parent_scope_id = data.boundary_scope.id
+}