Allow configuring nginx-ingress proxy buffer size
Summary
Per gitlab-org/gitlab#351181 (closed) and related to gitlab-org/omnibus-gitlab#6678 (closed), when using Geo proxying, we would replay the header from the primary in Workhorse, which can get pretty large in some cases, i.e. over 4k on the staging Geo site.
Proposal
We could configure the proxy-buffer-size in nginx-ingress to override the defaults (default == 4k) to allow for larger headers.
It looks like we could set the proxy-buffer-size in the configmap based on the ingress-nginx docs.