#1302 Rewrite SubSystemBoot as registered service. (state: open)

Description

This PR rewrites the SubSystemBoot class as registered service.

This PR fixes the error "The "logger" service or alias has been removed or inlined when the container was compiled. You should either make it public, or stop using the container directly and use dependency injection instead."

I needed to inject the logger service because it is not public.

Checklist

• Read and understood the CONTRIBUTING guidelines
• Created tests, if possible
• All tests passing
• Extended the README / documentation, if necessary
• Added myself to the @authors in touched PHP files
• Checked the changes with phpcq and introduced no new issues

Most of the times, I am on the latest versions, so this should've been Contao 4.7.4.

So logger became private somewhere between 4.4 and 4.7, good to know - I think I have some other places where it was being used via fetching from container.