Forced response cache revalidation on logged-in responses

- Prevents authenticated responses being visible when back button
  pressed in browser.
- Previously, 'no-cache, private' was added by default by Symfony which
  would have prevents proxy cache issues but this adds no-store and a
  max-age option to also invalidate all caching.

Thanks to @haxatron via huntr.dev
Ref: https://huntr.dev/bounties/6cda9df9-4987-4e1c-b48f-855b6901ef53/

app/Http/Kernel.php

@@ -2,6 +2,7 @@
 
 namespace BookStack\Http;
 
+use BookStack\Http\Middleware\PreventAuthenticatedResponseCaching;
 use Illuminate\Foundation\Http\Kernel as HttpKernel;
 
 class Kernel extends HttpKernel
@@ -30,6 +31,7 @@ class Kernel extends HttpKernel
             \Illuminate\Session\Middleware\StartSession::class,
             \Illuminate\View\Middleware\ShareErrorsFromSession::class,
             \BookStack\Http\Middleware\VerifyCsrfToken::class,
+            \BookStack\Http\Middleware\PreventAuthenticatedResponseCaching::class,
             \BookStack\Http\Middleware\CheckEmailConfirmed::class,
             \BookStack\Http\Middleware\RunThemeActions::class,
             \BookStack\Http\Middleware\Localization::class,
@@ -39,6 +41,7 @@ class Kernel extends HttpKernel
             \BookStack\Http\Middleware\EncryptCookies::class,
             \BookStack\Http\Middleware\StartSessionIfCookieExists::class,
             \BookStack\Http\Middleware\ApiAuthenticate::class,
+            \BookStack\Http\Middleware\PreventAuthenticatedResponseCaching::class,
             \BookStack\Http\Middleware\CheckEmailConfirmed::class,
         ],
     ];