DEV: Convert email_in_min_trust to groups (#24515)

This change converts the `email_in_min_trust` site setting to
`email_in_allowed_groups`.

See: https://meta.discourse.org/t/283408

- Hides the old setting
- Adds the new site setting
- Add a deprecation warning
- Updates to use the new setting
- Adds a migration to fill in the new setting if the old setting was
  changed
- Adds an entry to the site_setting.keywords section
- Updates tests to account for the new change

After a couple of months we will remove the
`email_in_min_trust` setting entirely.

Internal ref: /t/115696

lib/site_settings/deprecated_settings.rb

@@ -18,6 +18,7 @@ module SiteSettings::DeprecatedSettings
       false,
       "3.3",
     ],
+    ["email_in_min_trust", "email_in_allowed_groups", false, "3.3"],
   ]
 
   def setup_deprecated_methods