Add the ability to exclude remote users in user directory search results (#18300)

This change adds a new configuration
`user_directory.exclude_remote_users`, which defaults to False.
When set to True, remote users will not appear in user directory search
results.

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---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

docs/usage/configuration/config_documentation.md

@@ -4095,6 +4095,7 @@ This option has the following sub-options:
 * `prefer_local_users`: Defines whether to prefer local users in search query results.
    If set to true, local users are more likely to appear above remote users when searching the
    user directory. Defaults to false.
+* `exclude_remote_users`: If set to true, the search will only return local users. Defaults to false.
 * `show_locked_users`: Defines whether to show locked users in search query results. Defaults to false.
 
 Example configuration:
@@ -4103,6 +4104,7 @@ user_directory:
     enabled: false
     search_all_users: true
     prefer_local_users: true
+    exclude_remote_users: false
     show_locked_users: true
 ```
 ---