mod_rest: Wrap webhook setup in a function for future reuse The goal is to allow binding a session to a webhook via API to allow e.g. bots to set up handling of incoming messages.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```