Lowering Envoy's cluster per-connection buffer to 32kb

[davecheney]

Envoy allocates 1mb per connection to a backend pod.

https://www.envoyproxy.io/docs/envoy/latest/api-v2/api/v2/cds.proto#cluster

It is not clear if it allocates it all in one go, or it is an upper limit. In either case 1Mb is a lot. I think it should be lowered to something like 64kb.

[youngnick]

I've updated the title to reflect the recommendations from #1375.

[youngnick]

From the Envoy documentation, this is a soft limit, not a hard limit, so we should be fine to set this to 32KiB.

[davecheney]

@youngnick agreed.

[davecheney]

Based on https://github.com/projectcontour/contour/pull/1797#pullrequestreview-306974148 I think this setting doesn't do what I thought it did. Moving to the backlog for further investigation.