Don't apply security.require-https to intracluster requests

Summary:
Ref T10784. Currently, if you terminate SSL at a load balancer (very common) and use HTTP beyond that, you have to fiddle with this setting in your premable or a `SiteConfig`.

On the balance I think this makes stuff much harder to configure without any real security benefit, so don't apply this option to intracluster requests.

Also document a lot of stuff.

Test Plan: Poked around locally but this is hard to test outside of a production cluster, I'll vet it more thoroughly on `secure`.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10784

Differential Revision: https://secure.phabricator.com/D15696

src/docs/user/cluster/cluster_databases.diviner

@@ -301,6 +301,18 @@ it says to do:
 
 TODO: Make `bin/storage dump` replica-aware. See T10758.
 
+With recent versions of MySQL, it is also possible to configure a //delayed//
+replica which intentionally lags behind the master (say, by 12 hours). In the
+event of a bad mutation, this could give you a larger window of time to
+recognize the issue and recover the lost data from the delayed replica (which
+might be quick) without needing to restore backups (which might be very slow).
+
+Delayed replication is outside the scope of this document, but may be worth
+considering as an additional data security step on top of backup snapshots
+depending on your resources and needs. If you configure a delayed replica, do
+not add it to the `cluster.databases` configuration: Phabricator should never
+send traffic to it, and does not need to know about it.
+
 
 Next Steps
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