Roster Subscription Pre-Approval

[sstrigler]

Implementation of RFC 6121 section 3.4: Pre-Approving a Subscription Request https://datatracker.ietf.org/doc/html/rfc6121#section-3.4

To initiate before anything else, a person that wants to smoothly add a new contact for some other person or bot sends

<presence type='subscribed' to='other@some_host.tld' id='123'/>

Then proceeds with regular subscription request. If the other entity replies with their own subscription request, our server will then automatically approve it.

Changes in SQL schema

A new column approved of type boolean is added to rosterusers.

ALTER TABLE `rosterusers` ADD COLUMN `approved` boolean NOT NULL AFTER `subscription`;

[coveralls]

coverage: 18.402% (-16.0%) from 34.354%
when pulling 7650acc on sstrigler:roster-pre-approval
into b703375 on processone:master.