wmf: Script to dynamically generate tenant config
Include a script for use as a scheduler.tenant_config_script
that
fetches a core tenant config from a GitLab repo and amends it to include
untrusted projects for all projects under the given namespaces.
This should allow us to implement a policy where projects under some specific GitLab namespaces will be using Zuul.
Bug: T351329 Change-Id: Ia7c42b71993bacad2169859e2d6f6eb2bdf63ed8