Unattended Upgrade Enhancements

## Description

This patch improves the reliability of the Unattended-Upgrades subsystem.
While the currently active PHP version is already up-to-date, this patch will also upgrade the inactive PHP packages, along with several other supporting packages.
The patch doesn't upgrade any packages itself, upgrades happen during the next scheduled unattended-upgrades.

## Impact

On a single server deployment (All-In-One), PHP-FPM restarts once, which may interrupt requests for a few seconds.
On an Cluster, the web `leader` and the Varnish `leader` are used to create an updated boot image and worker nodes are replaced from using the Auto-Scaling mechanism.  No downtime is expected during the roll out of the updated image.

Your database and other nodes are not impacted.

## Changes

- Configures unattended-upgrades refresh the PHP packages that aren't in use and several other supporting packages
- Restart PHP-FPM on web nodes
- On clusters, backs up the web/Varnish leader, replaces web/Varnish nodes.

## If You Accept

Unattended upgrades keeps PHP and its supporting packages up to date automatically, including the PHP versions you aren't using.
Your sites and PHP settings are not impacted.

## If You Reject

PHP and other packages on your deployment can stop getting updates automatically.
Security fixes for them will lag behind until they're upgraded some other way.

Due `Critical` patch rating, it is not possible to reject this patch.