[FR]: Add "fleet" property to GKE Modules

[danistrebel]

The feature request

Allowing optional fleet to be specified in the GKE module would make the GKE clusters "born in the fleet" and make it automatically inherit fleet properties without additional fleet sync.

See Fleet membership docs here: https://cloud.google.com/kubernetes-engine/docs/concepts/configuration-overview#fleet-membership

Proposed solution

add "fleet" variable to

• modules/gke-cluster-autopilot
• modules/gke-cluster-standard

variable "fleet" {
  description = "The name of the Fleet host project where this cluster will be registered."
  type        = string
  default     = null
}

And populate the fleet variable of the container_cluster resource docs

Additional context

No response