feat(uxp): bump uxp to v1.15.x

[haarchri]

Description of your changes

• bump uxp version to v1.15.x to use registry feature
• remove registries for provider-helm and provider-kubernetes

Fixes #

I have:

• [x] Read and followed Upbound's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.
• [x] Added backport release-x.y labels to auto-backport this PR, as appropriate.

How has this code been tested

_output/bin/darwin_arm64/up space init 1.2.4 --token-file=/Users/haarchri/.aws/spaces-pull.json
 INFO  Setting defaults for vanilla Kubernetes (type kind)
 WARNING  One or more required prerequisites are not installed:

❌ cert-manager
❌ universal-crossplane
❌ ingress-nginx
❌ provider-kubernetes
❌ provider-helm

Would you like to install them now? [y/N]: Yes

  ✓   [1/5]: Installing cert-manager                                                                                                  
  ✓   [2/5]: Installing universal-crossplane                                                                                          
  ✓   [3/5]: Installing ingress-nginx                                                                                                 
  ✓   [4/5]: Installing provider-kubernetes                                                                                           
  ✓   [5/5]: Installing provider-helm                                                                                                 
 INFO  Required prerequisites met!

helm list -A
NAME                    NAMESPACE       REVISION        UPDATED                                 STATUS          CHART                                   APP VERSION
universal-crossplane    upbound-system  1               2024-04-25 11:28:46.060963 +0200 CEST   deployed        universal-crossplane-1.15.2-up.1        1.15.2-up.1

kubectl get pkgrev
NAME                                                                                     HEALTHY   REVISION   IMAGE                                            STATE    DEP-FOUND   DEP-INSTALLED   AGE
providerrevision.pkg.crossplane.io/crossplane-contrib-provider-helm-839e04a83ec3         True      1          crossplane-contrib/provider-helm:v0.17.0         Active                               2m53s
providerrevision.pkg.crossplane.io/crossplane-contrib-provider-kubernetes-6ef2ebb6f1db   True      1          crossplane-contrib/provider-kubernetes:v0.12.1   Active                               3m

[haarchri]

@turkenh can you merge this PR ?