Add docs about `kubectl otel`

[agardnerIT]

There is a Kubernetes plugin called kubectl otel which invokes tracepusher.

https://github.com/agardnerit/kubectl-otel

Document this

[agardnerIT]

This is on hold because there's some things to be cleared up in order to align the krew and the OTEL folks.

Krew is saying they won't / don't / can't approve the otel name. @austinlparker (one of the OTEL maintainers) doesn't believe the project reserves otel and thus can't see an issue with using the term otel. Austin will bring it up at the next OpenTelemetry governance committee.

Until then, we'll put this on hold pending the outcome of the discussion.

[agardnerIT]

I've requested an update from krew on that PR. Let's see what happens.