Set max_files to 4096 for image cache

This should prevent the warning:

> Warning: The directory '/var/cache/smokeping/images' contains 1027 entries, which exceeds the default soft limit 1000 and may cause excessive resource consumption and degraded performance. To remove this warning set a value for `max_files` parameter or consider using an alternate method to manage large directory trees

Also see https://www.puppet.com/docs/puppet/7/types/file.html#file-attribute-max_files

We may be able to revert this in v7.0.0, which introduces an option
to not manage the image cache:

* voxpupuli#145
* voxpupuli#146

manifests/install.pp

@@ -31,10 +31,11 @@
     recurse => true,
   }
   file { $smokeping::path_imgcache:
-    ensure  => directory,
-    owner   => $smokeping::webserver_user,
-    group   => $smokeping::webserver_group,
-    require => Package['smokeping'],
-    recurse => true,
+    ensure    => directory,
+    owner     => $smokeping::webserver_user,
+    group     => $smokeping::webserver_group,
+    require   => Package['smokeping'],
+    recurse   => true,
+    max_files => 4096,
   }
 }