Require `encoding` option for console and file sinks

The dynamic encoding concept in Vector was confusing users, so we've made it required and explicit. Simply add encoding.codec = "json" to your console and file sinks.

Upgrade Guide

Make the following changes in your vector.toml file:

 [sinks.console]
   type = "console"
+  encoding.codec = "json"

 [sinks.file]
   type = "file"
+  encoding.codec = "json"

That's it!