Fix/aks: Use new url for icon

[mqasimsarfraz]

Before this change:

✅ Name is valid                                                                                                                                                                                                                                                                                                                                                                                                      
✅ Directory is valid
✅ Secrets are valid
✅ Config env is valid
✅ License is valid
🛑 Icon could not be fetched, status code: 404, url: https://raw.githubusercontent.com/Azure/AKS/master/blog/assets/images/400x400.png
✅ Remote validation skipped (not a remote server)
✅ OAuth dynamic configuration is valid

After this change:

→ task validate -- --name aks
task: [validate] go run ./cmd/validate --name aks
✅ Name is valid                                                                                                                                                                                                                                                                                                                                                                                                      
✅ Directory is valid
✅ Secrets are valid
✅ Config env is valid
✅ License is valid
✅ Icon is valid
✅ Remote validation skipped (not a remote server)
✅ OAuth dynamic configuration is valid

[mqasimsarfraz]

Can I please get a review on this, it is just a logo change! 🙈 (pinned the url so we don't have an issue for it)

cc: @ipedrazas / @slimslenderslacks