Clear redis cache and precompile assets during update to 6.0. Fix #4874 #4840

As a consequence on the namespaces change from 5.4 to 6.0, after upgrade lots of links on the dashboard were not working (pointing to projects without the group part on the url).

Also, after upgrading to 6.0-stable, the network (branch history) function does not work. The progress bar rotates forever, but the network graph cannot be generated.
    
Clearing redis cache reportedly fixed those issues.