New compression options for some sinks

Stuff more data down a smaller hose in less time for cheaper.

Several sinks, including most AWS sinks as well as Humio and New Relic have had compression options added.

Enabling Compression

Compression is opt-in. Make the following changes in your vector.toml file:

    type = "aws_cloudwatch_metrics" # required
    inputs = ["big-firehose"] # required
    healthcheck = true # optional, default
    namespace = "service" # required
    region = "us-east-1" # required, required when endpoint = ""
+   compression = "gzip" # optional, default none