Crossplane installation fails if there is no direct internet connectivity

Summary

When sylva is deployed without internet connectivity using registry mirrors, crossplane unit installation fails:

2025/12/12 10:44:21.884574 Kustomization/crossplane state changed: HealthCheckFailed - health check failed after 30.051611882s: timeout waiting for: [CustomResourceDefinition/providerconfigs.keycloak.crossplane.io status: 'NotFound']
2025/12/12 10:45:22.042134 Kustomization/crossplane state changed: Progressing - Reconciliation in progress
2025/12/12 10:45:24.307786 Unit timeout exceeded: unit Kustomization/crossplane did not became ready after 5m0s
Details on Kustomization/crossplane and related resources:
IDENTIFIER                            STATUS     REASON      MESSAGE
Kustomization/sylva-system/crossplane InProgress             Kustomization generation is 2, but latest observed generation is -1
╰┄╴┬┄┄[Conditions]
   ├┄╴Reconciling                     True       Progressing Running health checks for revision 0.0.0-git-aba8a12e@sha256:d3d70295d2c6d5fc3c151833aa6bc77d5d4e03aa5fc5a98d86cd689efd4ea17e with a timeout of 30s
   ├┄╴Ready                           Unknown    Progressing Reconciliation in progress
   ╰┄╴Healthy                         Unknown    Progressing Running health checks for revision 0.0.0-git-aba8a12e@sha256:d3d70295d2c6d5fc3c151833aa6bc77d5d4e03aa5fc5a98d86cd689efd4ea17e with a timeout of 30s

This is probably caused by the hardcoding of the reqistry in provider configuration.