Allow setting enableServiceLinks to false in etcd and syncer

[cezar-guimaraes]

What happened?

We are experimenting using vcluster to shard a cluster with 10K+ services between multiple vclusters.

It has been working perfectly for 2 weeks but we hit the first issue today: the etcd statefulset and the syncer deployment died and failed to start up due to there being too many environment variables. This is a known issue in clusters with too many services, and the workaround we usually employ is to disable pod's service links, as each service ends up as another environment variable to a pod.

Currently, however, there is no way to disable service links in the k8s chart
https://github.com/loft-sh/vcluster/blob/v0.19/charts/k8s/templates/etcd-statefulset.yaml

Edit to add: we have disabled service links manually in the etcd statefulset and syncer deployment and everything seems to be working.

What did you expect to happen?

Either:

• for enableServiceLinks to be set to false (if vcluster does not work without DNS service discovery in the host cluster, I don't think there is a reason to leave that to the default true value)
• a chart value allowing service links to be disabled

How can we reproduce it (as minimally and precisely as possible)?

Create 10K+ services in a cluster.

k get svc -A | wc -l
15405

Anything else we need to know?

I could open a PR for this (or for the related #1622 which would also fix this issue for us). I just see the charts on the v0.19 branch, is that the branch a potential PR should target?

Host cluster Kubernetes version

$ kubectl version
Client Version: v1.28.0
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.25.16-eks-b9c9ed7
WARNING: version difference between client (1.28) and server (1.25) exceeds the supported minor version skew of +/-1

Host cluster Kubernetes distribution

# Write here

vlcuster version

$ vcluster --version
vcluster version 0.19.5

Vcluster Kubernetes distribution(k3s(default)), k8s, k0s)

k8s

OS and Arch

OS: linux
Arch: amd64

[FabianKramm]

@cezar-guimaraes thanks for creating this issue! Yes I think we can add that option