Bug: Fix Compute Disk Snapshot Schedule

[ronballesteros]

This PR updates the compute disk snapshot schedule module as right now it is requiring all 3 schedule types to be added (see below).

│ Error: Invalid value for input variable
│ 
│   on gcp-snapshots.tf line 26, in module "lnd_lab_disk_snapshots":
│   26:   snapshot_schedule = {
│   27:     daily_schedule = {
│   28:       days_in_cycle = 1
│   29:       start_time    = "04:00"
│   30:     }
│   31:   }
│ 
│ The given value is not suitable for module.lndus_disk_snapshots.var.snapshot_schedule declared at .terraform/modules/lndus_disk_snapshots/modules/compute_disk_snapshot/variables.tf:42,1-29:
│ attributes "hourly_schedule" and "weekly_schedule" are required.

The error I'm encountering indicates that only one of daily_schedule, weekly_schedule, or hourly_schedule can be specified in a single google_compute_resource_policy resource's schedule block.

More info: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_resource_policy#nested_snapshot_schedule_policy

snapshot_schedule = {
    daily_schedule = {
      days_in_cycle = 1
      start_time    = "04:00"
    }
    hourly_schedule = {
      hours_in_cycle = 20
      start_time     = "23:00"
    }
    weekly_schedule = {
      day_of_weeks = [
        {
          day        = "MONDAY"
          start_time = "23:00"
        }
      ]
    }
  }

│ "snapshot_schedule_policy.0.schedule.0.weekly_schedule": only one of
│ `snapshot_schedule_policy.0.schedule.0.daily_schedule,snapshot_schedule_policy.0.schedule.0.hourly_schedule,snapshot_schedule_policy.0.schedule.0.weekly_schedule` can be specified, but
│ `snapshot_schedule_policy.0.schedule.0.daily_schedule,snapshot_schedule_policy.0.schedule.0.hourly_schedule,snapshot_schedule_policy.0.schedule.0.weekly_schedule` were specified.

Updated the snapshot variable to ensure that exactly one of daily_schedule, hourly_schedule, or weekly_schedule is provided. It uses a validation rule to enforce that only one of these schedules is specified at a time, preventing any combination of multiple schedules. If none or more than one schedule type is provided, it triggers an error.

Error: Invalid value for variable
│ 
│   on gcp-snapshots.tf line 26, in module "lndus_disk_snapshots":
│   26:   snapshot_schedule = {
│   27:     daily_schedule = {
│   28:       days_in_cycle = 1
│   29:       start_time    = "04:00"
│   30:     }
│   31:     hourly_schedule = {
│   32:       hours_in_cycle = 20
│   33:       start_time     = "23:00"
│   34:     }
│   35:     weekly_schedule = {
│   36:       day_of_weeks = [
│   37:         {
│   38:           day        = "MONDAY"
│   39:           start_time = "23:00"
│   40:         }
│   41:       ]
│   42:     }
│   43:   }
│     ├────────────────
│     │ var.snapshot_schedule.daily_schedule is object with 2 attributes
│     │ var.snapshot_schedule.hourly_schedule is object with 2 attributes
│     │ var.snapshot_schedule.weekly_schedule is object with 1 attribute "day_of_weeks"
│ 
│ Exactly one of daily_schedule, hourly_schedule, or weekly_schedule must be provided.
│ 
│ This was checked by the validation rule at .terraform/modules/lndus_disk_snapshots/modules/compute_disk_snapshot/variables.tf:70,3-13.

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[ronballesteros]

Just saw this from @bulowaty: #468. Looks like we're on the same page here.

[ronballesteros]

Can we get a review on this PR please?