Creating new configuration entries are not forwarded to the primary datacenter

[mkeeler]

Overview of the Issue

Neither the HTTP nor RPC APIs for applying a config entry will rewrite the target datacenter to send it to the configured primary datacenter. If they are applied in secondary dcs then this will lead to inconsistent state between datacenters as well as eventual removal as the config entry replication will see them as having been deleted in the primary.

Reproduction Steps

Steps to reproduce this issue, eg:

1. Create two datacenter cluster
2. `consul config write config.hcl