Improve error message presented when computeclass creation fails because of memory being present in resources/limits.

[sangee2004]

acorn version v0.10.0-rc2-9-g43dbcbf4+43dbcbf4

Steps to reproduce the problem:

1. Try to create computeclass with memory present in resources/limits

kind: ClusterComputeClass
apiVersion: admin.acorn.io/v1
default: false
metadata:
  name: cc-res-inv
description: Large compute for linux on arm64
cpuScaler: 0.75
supportedRegions:
 - local
memory:
  default: 20M
  min: 10M
  max: 100M
resources:
  limits:
    memory: 50M
    gpu-vendor.example/example-gpu: 2
  requests:
    gpu-vendor.example/example-gpu: 2

2. This fails as expected with following error message:

The ClusterComputeClass "cc-res-inv" is invalid: spec.resources.limits.memory: Invalid value: resource.Quantity{i:resource.int64Amount{value:50, scale:6}, d:resource.infDecAmount{Dec:(*inf.Dec)(nil)}, s:"50M", Format:"DecimalSI"}: Cannot specifiy spec.resources.limits.memory. Use explicit spec.cpuScaler and spec.memory instead

Expected Behavior:
Error message can be improved to be more readable in this case.