Support relative paths for FOLDER_ANNOTATION

[diversit]

Running into this issue when trying to replace the default Grafana sidecar by this one.

The Kiwigrid sidecar supports the path in the FOLDER_ANNOTATION value to be relative.
Its documentation says:

The annotation the sidecar will look for in configmaps to override the destination folder for files. 
The annotation value can be either an absolute or a relative path. Relative paths will be relative to FOLDER.

This sidecar does not seem to support relative paths:

[2021-11-05 13:03:44,649] kopf.objects         [ERROR   ] Failed to write file kubernetes/scheduler.json

I prefer to use relative paths so teams adding files via ConfigMaps don't have to be bothered with the actual path where the file is being copied. E.g. /tmp/dashboards in case of Grafana dashboards.

[OmegaVVeapon]

Fair request, should be fairly trivial to add.

[OmegaVVeapon]

Fix present in the latest release 1.4.0.

Thanks for the opening the issue @diversit !