"Switching to another layout" shortcut was not set by oem-config for end-user

Steps to reproduce:
1. Launch Ubuntu MATE 20.04 LTS installer in OEM mode
2. Confirm using English locale
3. While setting OS for end user specify Russian language, confirm system configuration
4. Login to the configured system

Expected result:
* the keyboard layout switcher shows two layouts - *en* and *ru*, reacts on <Alt>+<Shift> hotkey

Actual result:
* the keyboard layout switcher shows two layouts - *en* and *ru*, but does not react on <Alt>+<Shift> hotkey

Note: the contents of keyboard configuration files is the following:

```
$ cat /etc/default/keyboard
# KEYBOARD CONFIGURATION FILE

# Consult the keyboard(5) manual page.

XKBMODEL="pc105"
XKBLAYOUT="us,ru"
XKBVARIANT=","
XKBOPTIONS="grp_led:scroll"

BACKSPACE="guess"

```
so keyboard layout switcher is not defined here.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: keyboard-configuration 1.194ubuntu3
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu21
Architecture: amd64
CurrentDesktop: MATE
Date: Thu Apr 2 00:43:16 2020
InstallationDate: Installed on 2020-04-01 (0 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Beta amd64 (20200401)
PackageArchitecture: all
SourcePackage: console-setup
UpgradeStatus: No upgrade log present (probably fresh install)