Add 'sle-module-python3' to autoyast config file

[rfan1]

https://progress.opensuse.org/issues/157843

• Verification run: http://openqa.suse.de/tests/13856391

Addons:

<addons t="list">
<addon t="map">
<arch>x86_64</arch>
<name>sle-module-python3</name>
<reg_code/>
<release_type>nil</release_type>
<version>15.6</version>
</addon>
<addon t="map">
<arch>x86_64</arch>
<name>sle-module-server-applications</name>
<reg_code/>
<release_type>nil</release_type>
<version>15.6</version>
</addon>
<addon t="map">
<arch>x86_64</arch>
<name>sle-module-basesystem</name>
<reg_code/>
<release_type>nil</release_type>
<version>15.6</version>
</addon>
</addons>