Add a logging category for the backend
Summary:
To get rid of tons of logs like :
using... PackageKit::Transaction(0x55db7f249ab0) "/14940_dbaecdcb"
using... PackageKit::Transaction(0x55db7f33fba0) "/14940_dbaecdcb"
using... PackageKit::Transaction(0x55db7d97b860) "/14941_ecaeeebe"
Test Plan: builds
Reviewers: apol, ngraham, mlaurent
Reviewed By: apol, mlaurent
Subscribers: mlaurent, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D26533