Allow full error trace in Nunjucks

When a global function in a template throws an error, we don’t see the
full trace of the error, which makes diagnosing issues really hard.

This makes use of the [undocumented dev argument](mozilla/nunjucks#1430)
which allows us to see the cause of the error in our logs and in Sentry.

[Copied from CAS1.](ministryofjustice/hmpps-approved-premises-ui@8eed08b)

server/@types/nunjucks/index.d.ts

@@ -0,0 +1,7 @@
+export default {}
+
+declare module 'nunjucks' {
+  export interface ConfigureOptions {
+    dev?: boolean | undefined
+  }
+}

server/utils/nunjucksSetup.ts

@@ -57,6 +57,7 @@ export default function nunjucksSetup(app: express.Express, path: pathModule.Pla
     {
       autoescape: true,
       express: app,
+      dev: true, // This is set to true to allow us to see the full stacktrace from errors in global functions, otherwise it gets swallowed and tricky to see in logs
     },
   )