mod_pubsub_subscription: support subscribing from a bare JID Allow subscribing from a bare JID on the component instead of only the component host, useful for subscribing to whitelist access model nodes that want to see a particular JID in the from.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
modules_enabled = {
    -- other modules --
    "s2s_whitelist",

}
s2s_whitelist = {
    "example.org",
}
```