[QBS] Allow to use custom build configurations

A QBS support different build configurations (not only a 'debug' or 'release): https://doc-snapshots.qt.io/qbs/cli-build.html

For this purpose, to build an application, we can use the following command line:

qbs build config:my-cool-config-name

F.e. this code example:

import qbs

CppApplication {
    name: "HelloWorld-minimal"

    Properties {
        condition: qbs.configurationName === "debug"
        files: "main.cpp"
    }

    Properties {
        condition: qbs.configurationName === "foo"
        files: "foo.cpp"
    }

    Properties {
        condition: qbs.configurationName === "bar"
        files: "bar.cpp"
    }
}

can be built with this command lines:

qbs build config:debug
qbs build config:foo
qbs build config:bar

So, I expect, that adding to the "QtC -> Build Settings -> Edit Build configuration -> Add -> foo" will build my project with 'config:foo' property. But, but it is does not work as expected.

From QtC I see that an "equivalent command line" is:

C:\Qt-meta\Tools\QtCreator\bin\qbs.exe build -d D:\ng\foo -f D:\Git\ng\hello.qbs --settings-dir C:\Users\denis.DESKTOP-RN6J6RU\AppData\Roaming\QtProject\qtcreator --command-echo-mode command-line --jobs 12 config:Debug qbs.defaultBuildVariant:debug profile:qtc_Desktop__700541af

As you can see, there are 'config:Debug' instead of 'config:foo'.