Provide a container for building Envoy on Oracle Linux 8.

[michaelfinch]

Also add instructions about how to run an Oracle Linux 8 Envoy binary on a CentOS 7 host.

[phlax]

@michaelfinch i dont think this is something we have the capacity to maintain

[michaelfinch]

@michaelfinch i dont think this is something we have the capacity to maintain

Ack. So should I close this PR? If so my team will just maintain our own fork. I stumbled upon a number of threads with people wanting to run the latest Envoy versions on CentOS 7, so I figured it would be helpful to document instructions here.

[phlax]

the centos build still exists for legacy glibc reasons - some people are still ~actively using it so it has been kept - but as you can probably tell its not being actively maintained (nm tested)

i think we do need a solution for building with other toolchains/for other distributions but ideally using one container/os to do it, as that is already quite a bit of work