Change default threshold to view project doc to VIEWER

Previously it was ANYBODY, which would let any user download files from
any project including private ones, even when they are not part of the
team.

Backport from a4be76d

Fixes #19873

config_defaults_inc.php

@@ -2354,9 +2354,13 @@
 
 	/**
 	 * Threshold needed to view project documentation
+	 * Note: setting this to ANYBODY will let any user download attachments
+	 * from private projects, regardless of their being a member of it.
+	 * @see $g_enable_project_documentation
+	 * @see $g_upload_project_file_threshold
 	 * @global int $g_view_proj_doc_threshold
 	 */
-	$g_view_proj_doc_threshold = ANYBODY;
+	$g_view_proj_doc_threshold = VIEWER;
 
 	/**
 	 * Site manager