Implement SpinApp per-request invocation limits

[kate-goldenring]

• Implements SKIP 6: https://github.com/spinframework/skips/tree/main/proposals/006-spinapp-invocation-limits
• Adds validation check for the known "memory" limit

Tested with Spintainer executor:

apiVersion: core.spinkube.dev/v1alpha1
kind: SpinAppExecutor
metadata:
  name: spintainer
spec:
  createDeployment: true
  deploymentConfig:
    installDefaultCACerts: true
    spinImage: ghcr.io/spinframework/spin:v3.3.0
---
apiVersion: core.spinkube.dev/v1alpha1
kind: SpinApp
metadata:
  name: cpu-load-gen
spec:
  image: "ghcr.io/spinkube/spin-operator/cpu-load-gen:20240311-163328-g1121986"
  executor: spintainer
  replicas: 1
  invocationLimits:
    # memory: "10Mi" # Will succeed
    memory: "1000" # Will fail. Check Spintainer pod logs to see error: 2025-06-17T23:16:15.009686Z ERROR spin_trigger_http::server: Error processing request: memory minimum size of 2 pages exceeds memory limits