Add support for multiple KernelCI API backends
Parameterize the KernelCI API URL and rework the database and code so the tracker can use multiple different KernelCI API backends simultaneously, then track one of the ChromeOS-specific branches (we might want to review which branches to track).
NOTE: These changes alter the database structure, so the database needs to be rebuild from scratch after this is merged. To do that, run a complete pipeline with the CI variable "rebuild" set to "true".