Configure the extra options API call for Stackit

Changing the target project did not re-list the destination options,
because Stackit had no `extraOptionsApiCalls` entry. `availability_zone`
is its only prerequisite, and `project` scopes every resource the
provider lists, so it belongs in `relistFields`.

Signed-off-by: Mihaela Balutoiu <mbalutoiu@cloudbasesolutions.com>

config.ts

@@ -147,6 +147,12 @@ const conf: Config = {
       requiredFields: ["zone"],
       relistFields: ["linux_template", "windows_template"],
     },
+    {
+      name: "stackit",
+      types: ["destination"],
+      requiredFields: ["availability_zone"],
+      relistFields: ["project"],
+    },
   ],
 
   /*