De-gateway the providers

[kevin-bates]

The providers (and lifecycle managers) are no longer part of Enterprise Gateway. We need to make passes on the existing providers to remove/replace references to 'EG', 'Gateway', etc.

Per the existing convention, all environment variables should have a prefix. Today, that prefix is EG_ or KERNEL_. EG_ is used for system-owned entities and spans the process proxy code (kernel lifecycle managers in provider-land). KERNEL_ is used to convey information to the kernel and/or its launch and typically reflects information contained in the kernel startup payload coming from the client.

Clearly, we'll keep KERNEL_ in place for now (these may want to be converted to actual parameters once kernel-launch parameterization is in place).

For the system-owned EG_ prefix, I'd like to propose it be replaced with RKP_ independent of actual kernel provider. This way there is a consistency in place such that the admin really just need to know the primary (suffix) portion of the variable irrespective of the hosting provider (Yarn, Kubernetes, Docker, etc.).

As for other variables and comments, we should replace incantations of "gateway" or "enterprise gateway" with "application", "application server", "server", etc.

This effort should span the various kernel providers repos that derive from RemoteKernelProvider and will contain a similarly named issue that references this one.