mod_client_management: Add support for revocation of clients (when possible) We decided to keep the unified listing of "clients", which includes both SASL2 clients and OAuth grants, etc. To a user, or someone wanting to manage what can access their account, they are largely equivalent. To accomplish this technically, we add a prefix to the id to state what type it really is.

Generate a DNS UPDATE order in format suitable for `nsupdate` based on
current port configuration.

Example output:

```
$ prosodyctl mod_dnsupdate -d example.com -t xmpp.example.com example.com
zone example.com
server ns1.example.com
ttl 3600
add _xmpp-client._tcp.example.com IN SRV 1 1 5222
add _xmpp-server._tcp.example.com IN SRV 1 1 5269
```