Updates/upgrades won't run without AC power, despite explicit config

[James McKenzie]

Despite configuring unattended-upgrades to run on battery power, the script will only run automatically when on AC power due to a condition of the systemd apt-daily.service

Here is my current Unattended-Upgrades config (apt-config dump Unattended-Upgrade):
```
Unattended-Upgrade "";
Unattended-Upgrade::Allowed-Origins "";
Unattended-Upgrade::Allowed-Origins:: "${distro_id}:${distro_codename}";
Unattended-Upgrade::Allowed-Origins:: "${distro_id}:${distro_codename}-security";
Unattended-Upgrade::Allowed-Origins:: "${distro_id}ESMApps:${distro_codename}-apps-security";
Unattended-Upgrade::Allowed-Origins:: "${distro_id}ESM:${distro_codename}-infra-security";
Unattended-Upgrade::DevRelease "auto";
Unattended-Upgrade::OnlyOnACPower "false";
```

From testing I found that although unattended-upgrades run on battery power when manually called via the terminal, they do not get run automatically due to a condition check failure in the apt-daily.service

```
● apt-daily.service - Daily apt download activities
     Loaded: loaded (/lib/systemd/system/apt-daily.service; static; vendor preset: enabled)
     Active: inactive (dead)
TriggeredBy: ● apt-daily.timer
  Condition: start condition failed at Thu 2022-02-03 08:08:49 GMT; 8min ago
             └─ ConditionACPower=true was not met
       Docs: man:apt(8)

Feb 02 10:48:58 ubu20-n-0649f43030 systemd[1]: Condition check resulted in Daily apt download activities being skipped.
Feb 03 08:08:49 ubu20-n-0649f43030 systemd[1]: Condition check resulted in Daily apt download activities being skipped.
```

So despite explicitly configuring unattended-upgrades to run on battery power, apt-daily.service seems to have a conflicting condition as well which isn't changed. Perhaps this is a recent change, because as far as I could tell, unattended-upgrades were running correctly with this config until the last few days.

Below is some additional information which might be useful:
unattended-upgrades - version 2.3ubuntu0.1
apt - version 2.0.6
Ubuntu - version 20.04.3 LTS, Kernel 5.13.0-1012-oem

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: unattended-upgrades 2.3ubuntu0.1
ProcVersionSignature: Ubuntu 5.13.0-1012.16-oem 5.13.1
Uname: Linux 5.13.0-1012-oem x86_64
ApportVersion: 2.20.11-0ubuntu27.21
Architecture: amd64
CasperMD5CheckResult: pass
Date: Thu Feb 3 08:42:53 2022
InstallationDate: Installed on 2021-09-02 (153 days ago)
InstallationMedia: Ubuntu-Server 20.04.2 LTS "Focal Fossa" - Release amd64 (20210201.2)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: unattended-upgrades
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.apt.apt.conf.d.15update-stamp:
 // This file is managed by Puppet. DO NOT EDIT.
 APT::Update::Post-Invoke-Success {"touch /var/lib/apt/periodic/update-success-stamp 2>/dev/null || true";};
mtime.conffile..etc.apt.apt.conf.d.10periodic: 2021-09-02T11:49:45.980132
mtime.conffile..etc.apt.apt.conf.d.15update-stamp: 2021-09-02T11:46:39.152655