Simplify instance upgrade experience in Terraform modules

[bobbyiliev]

As per #8, currently, the upgrade mechanism exposes low-level CRD concepts like in_place_rollout, request_rollout, and force_rollout directly to end users. This might be unnecessarily complex for most use cases.

One way that we might be able to achieve this is to replace these fields with a simpler abstraction that focuses on user intent rather than implementation details. For example:

variable "instances" {
  type = list(object({
    # existing fields...
    version = string
    upgrade_strategy = optional(object({
      minimize_downtime = optional(bool, true)  # false = in-place, true = rolling update
      force = optional(bool, false)             # whether to force the upgrade
    }))
  }))
}

Example usage:

instances = [
  {
    name = "my-instance"
    version = "v0.130.3"
    upgrade_strategy = {
      minimize_downtime = true  # Use rolling updates
    }
  }
]

The module would handle the underlying CRD fields (request_rollout UUIDs, etc.) internally, abstracting these implementation details away from users.