Track usage of os.getenv('KCI_INSTANCE')`

This might cause some headache later when working with `localinstall` or other non-managed Maestro instances but should be fine in the current setup.

Usage of `os.getenv('KCI_INSTANCE', ...)` needs to be tracked and reduced over time, though.

_Originally posted by @pawiecz in https://github.com/kernelci/kernelci-core/pull/2763#discussion_r1913512016_

No files, tests, or entry points are named. Start by searching the repository for os.getenv('KCI_INSTANCE') and review each usage in the context of managed and localinstall Maestro instances. Done would require documenting the usages and reducing them, but the issue does not define a specific target.

Written by the indexing model from the issue text.