add context to bigquery module (#3388)

tests/modules/bigquery_dataset/context.tfvars

@@ -0,0 +1,37 @@
+context = {
+  custom_roles = {
+    myrole_one   = "organizations/366118655033/roles/myRoleOne"
+    myrole_two   = "organizations/366118655033/roles/myRoleTwo"
+    myrole_three = "organizations/366118655033/roles/myRoleThree"
+    myrole_four  = "organizations/366118655033/roles/myRoleFour"
+  }
+  iam_principals = {
+    mygroup = "group:test-group@example.com"
+    mysa    = "serviceAccount:test@test-project.iam.gserviceaccount.com"
+    myuser  = "user:test-user@example.com"
+    myuser2 = "user:test-user2@example.com"
+  }
+  locations = {
+    ew8 = "europe-west8"
+  }
+  project_ids = {
+    test = "foo-test-0"
+  }
+  tag_values = {
+    "test/one" = "tagValues/1234567890"
+  }
+}
+project_id = "$project_ids:test"
+id         = "dataset_0"
+location   = "$locations:ew8"
+iam = {
+  "$custom_roles:myrole_one" = [
+    "$iam_principals:myuser"
+  ]
+  "roles/viewer" = [
+    "$iam_principals:mysa"
+  ]
+}
+tag_bindings = {
+  foo = "$tag_values:test/one"
+}