mod_restrict_xmpp: Treat archive query as a read despite using iq-set XEP-0313 uses iq-set to initiate a query, but unlike many other uses of iq-set, this does not mutate anything on the server, so it should not be treated as a write request.

This module blocks configured queries that change server state.

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

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