config_error: Support passing arguments specifying the "go back" link.

Depending on the kind of config error being shown, different "go back"
links may be more appropriate.
We probably hard-coded /login/ for it, because these config errors are
most commonly used for authentication backend config error, where it
makes sense to have /login/ as "go back", because the user most likely
indeed got there from the login page.

However, for remote_billing_bouncer_not_configured, it doesn't make
sense, because the user almost surely is already logged in and got there
by clicking "Plan management" inside the gear menu in the logged in app.

(cherry picked from commit fcc3d88daf)

templates/zerver/config_error/container.html

@@ -22,7 +22,7 @@
 
                     <p>After making your changes, remember to restart
                     the Zulip server.</p>
-                    <p><a href=""> Refresh</a> to try again or <a href="/login/">click here</a> to go back to the login page.</p>
+                    <p><a href=""> Refresh</a> to try again or <a href="{{ go_back_to_url }}">go back to {{ go_back_to_url_name }}</a>.</p>
                 </div>
 
             </div>

zerver/views/errors.py

@@ -1,12 +1,22 @@
+from typing import Optional
+
 from django.conf import settings
 from django.http import HttpRequest, HttpResponse
 from django.shortcuts import render
 
 
-def config_error(request: HttpRequest, error_name: str) -> HttpResponse:
+def config_error(
+    request: HttpRequest,
+    error_name: str,
+    *,
+    go_back_to_url: Optional[str] = None,
+    go_back_to_url_name: Optional[str] = None,
+) -> HttpResponse:
     assert "/" not in error_name
     context = {
         "error_name": error_name,
+        "go_back_to_url": go_back_to_url or "/login/",
+        "go_back_to_url_name": go_back_to_url_name or "the login page",
     }
     if settings.DEVELOPMENT:
         context["auth_settings_path"] = "zproject/dev-secrets.conf"

zerver/views/push_notifications.py

@@ -234,4 +234,9 @@ def self_hosting_auth_not_configured(request: HttpRequest) -> HttpResponse:
         # is actually real.
         return render(request, "404.html", status=404)
 
-    return config_error(request, "remote_billing_bouncer_not_configured")
+    return config_error(
+        request,
+        "remote_billing_bouncer_not_configured",
+        go_back_to_url="/",
+        go_back_to_url_name="the app",
+    )