Add overcommit spec and status

[PhilippMatthes]

We want to reflect the overcommit ratio in the hypervisor crd. This is useful for cortex, so it can calculate how much space is left on a hypervisor. By default, it is assumed that the overcommit for each resource is set to 1. If anything else is specified, it will be reflected in the new effectiveCapacity status field by the kvm node agent. This will allow cortex to take control of the hypervisor overcommit ratio, for now statically, and in the future dynamically.

Summary by CodeRabbit

• New Features
  • Added resource overcommit capability allowing per-resource ratio configuration (CPU, memory) with validation enforcing minimum 1.0 ratio.
  • Introduced effective capacity reporting that reflects actual available capacity after overcommit adjustments.
  • Implemented standardized resource naming constants for improved consistency across resource management.