feat(content): add roof chunks to hospital roof

[chaosvolt]

Purpose of change

This belatedly makes the hospital roof a bit less empty, like I'd promised to do a while back.

Describe the solution

Set it to place infrastructure/utility chunks at a decent rate in each of the roof tiles not next to the helipad, idea being keep the extra utility stuff spaced away from it.

Additionally, set the space near the helipad to have a modest chance of spawning signs of former survivors having camped out on the roof, including a decent chance of the "help" chunk appearing.

Describe alternatives you've considered

Screm

Testing

1. Checked affected file for syntax and lint errors.
2. Ported JSON file to test build, load-tested, spawned in a hospital to look at the roof.

Additional context

Checklist