Currently, three different exchanges are used: `datawarehouse.kcidb`, `herder` and `webhooks` [1].

AC:

• [x] consistent publishing: proper routing keys and message-type header everywhere, with routing keys corresponding to future publish exchange names (cki.datawarehouse, cki.herder)
• [x] route dw and herder exchanges to webhooks exchange (as already done for fedmsg/irc/umb), and rename dw publish exchange to cki.exchange.datawarehouse to be consistent with routing keys
• [ ] switch listeners to webhooks exchange with proper routing keys and message-type checks
• [x] update documentation

[1] https://cki-project.org/docs/background/infrastructure/messaging/

Jira: CKI-7221