Add and implement iptables-wrapper-installer.sh

[Oats87]

#1317

Description

This PR implements the iptables-wrapper-installer.sh script from https://github.com/kubernetes-sigs/iptables-wrappers/

Release Note

Enable auto-switching between `iptables (nf_tables)` and `iptables (legacy)` in Flannel container image

[rikatz]

@Oats87 can you confirm putting iptables-wrappers works fine with CentOS 8? Do you need me to help testing this?

Thank you!!

[dmitry-irtegov]

@Oats87 can you confirm putting iptables-wrappers works fine with CentOS 8? Do you need me to help testing this?

I tested this in mixed cluster with RHeL 7 and 8 nodes (the nftables issue is common to both CentOS and RHeL).
Pure flannel with this patch works (i.e. correctly autodetects iptables mode) and passes https://github.com/sapcc/kube-detective connectivity test.
Update: cni-canal with calico 3.14.1 also works.

[rikatz]

Great, let me know if you need some tests also. On a side note I wasn’t aware of that “detective” and will take a look :)

[rajatchopra]

@AleksandrNull Can you review this PR? Thanks.

[AleksandrNull]

Looking into

[AleksandrNull]

Looks good to me!

[AleksandrNull]

@rajatchopra I think we should merge it.