Unable to find a proxy with BMC feature

When trying to use BMC support, Foreman needs a smart proxy with the BMC feature enabled. It first looks for a DHCP or TFTP proxy with BMC also enabled that manages the same subnet (an opportunistic search), else it will use the first BMC proxy it finds.

(It'd be good to improve the location/proximity logic: #3644 tracks this.)

Check that you have at least one smart proxy with BMC enabled, by setting ":bmc: true" in /etc/foreman-proxy/settings.yml and then refresh the feature list in Foreman via the smart proxies UI.