(core) Adding a flag for the UI to check if emails are enabled

Summary:
Front-end code can now test if emails are enabled
and hide some parts of UI based on it.

Test Plan:
Only secondery text was hidden on add users dialog.
Tested manually.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Subscribers: georgegevoian

Differential Revision: https://phab.getgrist.com/D4221

app/client/lib/ACUserManager.ts

@@ -16,6 +16,7 @@ import {
   cssMemberText,
 } from "app/client/ui/UserItem";
 import {createUserImage, cssUserImage} from "app/client/ui/UserImage";
+import {getGristConfig} from 'app/common/urlUtils';
 import {Computed, computed, dom, DomElementArg, Holder, IDisposableOwner, Observable, styled} from "grainjs";
 import {cssMenuItem} from "popweasel";
 
@@ -111,10 +112,9 @@ export function buildACMemberEmail(
         )),
       cssMemberText(
         cssMemberPrimaryPlus(t("Invite new member")),
-        cssMemberSecondaryPlus(
-          // dom.text(use => `We'll email an invite to ${use(emailObs)}`)
-          dom.text(use => t("We'll email an invite to {{email}}", {email: use(emailObs)})) // TODO i18next
-        )
+        getGristConfig().notifierEnabled ? cssMemberSecondaryPlus(
+          dom.text(use => t("We'll email an invite to {{email}}", {email: use(emailObs)}))
+        ) : null,
       ),
       testId("um-add-email")
     )