Upgrade Keycloak version

[ebariaux]

Current version is 23
Several high security vulnerabilities are reported on that version, we need to move to a newer version, would advice for the latest one.

[richturner]

@ebariaux I will pick this up and deal with updating the main repo to work with this version

[ebariaux]

@richturner I already did some work on this, still need to commit

[ebariaux]

Pushed to feature/upgrade_26, no testing besides fact it compiles and docker build

[richturner]

Thanks @ebariaux I only want to pick up because getting the manager to v26 is problematic and some projects may well be pulling latest keycloak image automatically so I wanted to align the releases.

[ebariaux]

Also see #1840