Workload identity federation integrations should fit into meshplatform modules

[henryde]

meshstack_integrations data source has a computed attribute which contains all the information about workload identity federation. This field should be restructured so it fits nicely into the meshplatform modules.

Example:

module "meshplatform" {
  source  = "meshcloud/meshplatform/aks"
  
  # current state
  workload_identity_federation = {
    issuer         = data.meshstack_integrations.integrations.workload_identity_federation.replicator.issuer
    access_subject = data.meshstack_integrations.integrations.workload_identity_federation.replicator.subject
  }

  # better
  workload_identity_federation = data.meshstack_integrations.integrations.workload_identity_federation.aks
}