Add support for forward input

[tjamet]

In order to place the sumologic integration in a broader fluentd
infrastructure, add support the forward protocol, allowing to aggregate
logs from several external sources, send all in one place to sumologic.

[bin3377]

Is there any strong reason to include this input in master branch? Looks like there is no such input dependency so far in this repo?

[tjamet]

The motivation to do so is to allow using this same image in a context where the logs are collected by a light weighted daemon set (hosted by fluentbit for instance) and forwarded to a single place sending them to sumologic

In case of large deployments this would allow better usage and reservation of resources by scaling out, on demand, the sumologic forwarder deployment

It made sense, for me, to include it in this repo, providing an image runnable in kubernetes, used, as far as I understand, in the official sumologic-fluentd chart

[bin3377]

It should be ok to add this in. Could you update the readme for the new parameters and possible an example please?