Abstract common sink values

[chrisjohnson]

Being able to abstract some common sink values (like vaultBaseURL) seems handy when defining multiple sinks.

I had the thought to add some sinkDefaults key and then the configparser would just merge it into each sink. However I'm wondering if the golang yaml lib we are using supports yaml anchors out of the box. That would let us do something like this:

defaults: &defaults
  vaultBaseURL: https://cjohnson-kv.vault.azure.net

sinks:
 - <<: *defaults
  name: test
  etc: whatever

(or whatever the syntax is)