Add ActivityAnswer plugin

Added the stub config entities.

Needs an event subscriber similar to the one in lms_xapi_lesson: https://git.drupalcode.org/project/lms_xapi/-/blob/1.0.x/modules/lms_xap... since 📌 Allow more flexible identifiers for LRS entries Active landed.. or we can switch to tagged services and use that instead..

Or we can make all that follow-ups, just switch back to review then and I'll merge.

I think this now might be OK with the fallback logic in https://git.drupalcode.org/project/lms_xapi/-/blob/1.0.x/src/TincanServi...

Or.. if we wanted to add the course status in there, then I think we would want identical logic to https://git.drupalcode.org/project/lms_xapi/-/blob/1.0.x/modules/lms_xap...

So this either needs nothing extra, or we need to decide whether to copy and paste that logic, or move it to a trait somewhere for the modules to share - so moving to needs review for an opinion.

Added the generator, turns out there's very little shared logic with the lesson generator anyway, so was no point worrying about a trait.

Looks good, thanks!