Clarify for the user that page permissions settings are applied across all locales, unlike other page settings

Apostrophe 2.102.3

## To Reproduce

Step by step instructions to reproduce the behavior:

> 1. Go to Home page
> 2. Click on Page Settings > Permissions > Who Can View this page? > LoginRequired
> 3. Save the Settings
> 4. This Setting change is reflected across all the locales of the Home Page

## Expected behavior
> A change in the Login Required in pages between Locales should be independent

## Describe the bug
> Login Required changed in one locale page is reflected across all the locale pages. Ideally we were expecting it to reflect only in one page.

## Details

**Version of Node.js:**
10.24.1

**Server Operating System:**
Amazon Linux 2

**Additional context:**
> Add any other context about the problem here. If the problem is specific to a browser, OS or mobile device, specify which.

**Screenshots**

Start at the Home page's Page Settings > Permissions > Who Can View this page? flow and reproduce the LoginRequired change across locales. Determine whether permissions are intentionally shared or should be locale-specific; update the relevant behavior or user-facing clarification, then verify the result for multiple locale pages.

Written by the indexing model from the issue text.