Restrict SSH access to cluster VMs

[simu]

Summary

We want to restrict SSH access (port 22) to the cluster VMs. SSH access to the cluster VMs should only be allowed from the two LBs instead of allowing SSH access to all nodes from anywhere.

Acceptance criteria

• SSH access to cluster VMs only allowed from LBs
• Commodore component updated to use latest version of the Terraform module
• Rolled out for all clusters managed with the Terraform module (shouldn't need maintenance, since the security group rules are managed individually)

Implementation ideas

• Change the ssh access security group rules to allow access to the LBs from anywhere, and to allow access to the other nodes only from the LBs. Current security group rules: https://github.com/appuio/terraform-openshift4-exoscale/blob/a9df9ca2a0329ebe8d958afa635b636735728138/security_groups.tf#L68-L88

[simu]

Implemented in https://github.com/appuio/terraform-openshift4-exoscale/pull/89

(this is primarily a comment to test whether our Jira integration works again)