Add europe-west12 GCP region as supported region

Author: makentenza

modules/installation-gcp-regions.adoc

@@ -31,6 +31,7 @@ regions:
 * `europe-west6` (Zürich, Switzerland)
 * `europe-west8` (Milan, Italy)
 * `europe-west9` (Paris, France)
+* `europe-west12` (Turin, Italy)
 * `me-west1` (Tel Aviv, Israel)
 * `northamerica-northeast1` (Montréal, Québec, Canada)
 * `northamerica-northeast2` (Toronto, Ontario, Canada)