Remove deprecated SSL settings from HTTP poller input

[robbavey]

• Create branch from most recent commit on main
• All plugin changes that remove SSL settings should be in a new major release Mark previously deprecated SSL settings as obsolete #149
• Mark old SSL settings as obsolete
• Add details of change to the 9.0 breaking changes documentation in core. Add logstash-input-http_poller obsolete ssl section to breaking changes doc elastic/logstash#16792
• Add breaking change entry to plugin changelog
• Verify that any integration tests in core that rely on SSL settings still work. Fix any broken integration tests
• Verify plugin documentation, remove any references to deprecated settings