Check cluster size to check if stack/demos fits on k8s cluster

[sbernauer]

During installation of a stack or demo stackablectl should sum up the available resources (cpu + ram) of the k8s nodes.
Each stack and demo must provide the resource requirements - if not specified we e.g. default to 4 cores and 8 gb ram.
If the resources are not available a warning should be shown. (Alternative solution could be to error out and add a flag to force the installation)

[Techassi]

Added in stackabletech/stackable-cockpit#94