Expose http(s) port number setting via httpboot plugin
Foreman core needs this to setup boot URL correctly.
Refs #27654 - Move HTTP enabled logic to plugin settings
This introduces simple helpers to be used elsewhere. The Plugin Settings
class makes more sense for this since it's specific to a plugin setting.
Refs #27654 - Account for module enabled over http or not
The module can be enabled for http-only while the proxy is https-only
(or other combinations). This patch takes the enabled setting into
account and guarantees that the http_port is only set when the module is
actually available over http. The same goes for https_port.