net-mgmt/omada5: Fix mongodb configuration

The omada.properties config file was missing the override to force
mongodb to be externally managed which caused the daemon to fail to start.

The controller cannot manage mongodb by itself when running on FreeBSD so this
has always been a requirement that was mistakenly absent from the port.

Also fix ownership of some files and directories served by the controller's
webserver as an internal process automatically downloads icons for
newly released TP-Link hardware models and fills the log with errors if
the directory and files are not writable.

MFH: 2026Q2
(cherry picked from commit b8c78c0e013b32058307de5c37a9d8d30aa5f4ad)