Since Prosody 0.11, XEP-0410 is natively supported by Prosody, you will be redirected shortly.
This module implemented the Server Optimization part of XEP-0410: MUC Self-Ping
With the plugin installer in Prosody 0.12 you can use:
sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_muc_ping
For earlier versions see the documentation for installing 3rd party modules