Upgrade our development infrastructure to 15.6

[danidoni]

Now that https://build.opensuse.org is using 15.6. We need to ensure our development infrastructure uses the same version for development, testing, ci, integrations, etc.

• Upgrade our CI pipeline: Done here Upgrade our CI to run against 15.6 #16546
• Upgrade our Integrations: Done in the previous PR also.
• Upgrade our containers for development and test: Done here https://build.opensuse.org/request/show/1189429
• Ensure OBS:Server:Unstable:Containers has the base distros for 15.6 https://build.opensuse.org/projects/OBS:Server:Unstable:Containers/meta
• Provide a chromium for 15.6 https://build.opensuse.org/package/show/OBS:Server:Unstable/chromium.sle15sp6
• Point Kurren to the new version Update the monitoring configuration for 15.6 kurren#224