Disable automatic upgrade mode and implement upgrade policies

[rswrz]

Description

Changes include disabling the automatic upgrade mode and setting a scale-in policy to the oldest VM. Additionally, new variables for upgrade modes and policies have been introduced, along with sorting of VMSS parameters and removal of unnecessary custom data for instance upgrades.

This change prepares the Launchpad for a two-stage upgrade process. Together with upcoming changes in our IaCv3 deployment workflows, this enables safer and more controlled VMSS upgrades.

1. The VMSS will be configured with upgrade_mode = "Manual" by default (handled by this PR). This prevents automatic replacement of VMSS instances during configuration changes.

2. VMSS instances will be upgraded manually via az CLI. This will be handled by our IaCv3 deployment workflows.

   Example CLI for upgrading outdated VMSS instances:

    rg=rg-launchpad-01
    vmss=vmss-launchpad-prd-gwc
   
    outdated_instance_ids=$(az vmss list-instances \
      --name "$vmss" \
      --resource-group "$rg" \
      --query "[?latestModelApplied==\`false\`].instanceId" \
      --output tsv)
   
    for id in $outdated_instance_ids; do
      az vmss update-instances \
        --name "$vmss" \
        --resource-group "$rg" \
        --instance-ids "$id"
    done

PR Checklist

• I have checked if my changes close any open issues. If so please include appropriate closing keywords below.
• I have updated/added documentation written in a helpful and kind way to assist users that may be unfamiliar with the resource / data source.
• I have checked for a proper tag for this PR: breaking-change, feature, fix, other, ignore-release
• I have used a meaningful PR title to help maintainers and other users understand this change and help prevent duplicate work.

Motivation and Context

Closes #19.

Breaking Changes

No breaking changes. Existing deployments must explicitly set var.upgrade_mode, var.rolling_upgrade_policy, and var.automatic_os_upgrade_policy to avoid Terraform drift causing a recreation of the VMSS resource.