Make reload dependency aware

[sylvesterdamgaard]

Summary

• reload changed/removed processes in dependency-safe shutdown order
• restart new/changed processes in the new topological startup order
• unregister and re-register scheduled jobs during reload so stale jobs do not survive config changes
• add a focused regression test for nginx depending on php-fpm during reload startup

Verification

• git diff --check
• go test ./internal/process could not be run locally: go is not installed in this environment