[Meta] Remove deprecated SSL settings from core and plugins

[robbavey]

In #14905, we embarked on a process to standardize SSL settings across Logstash and its plugins.

We should continue this process by obsoleting old, deprecated settings for the 9.0 release of Logstash

Problem Statement

During https://github.com/elastic/ingest-dev/issues/1340, we embarked on a standardization process of SSL Settings, and added standardized settings to Logstash-core, and our most used plugins.
During that process, we deprecated the old settings, keeping both sets of settings in place to provide continuity.

The next phase of this plan is to remove the old deprecated settings for the 9.0 release - the old settings have been marked as deprecated for over 18 months, and having two sets of settings for these products may be confusing for users.

We should go through the process of removing the old settings, marking them as obsolete.

Each Change needs to:

Core

• Ensure that all unit and integration tests still pass
• Add details of change to the 9.0 breaking changes documentation in core.

Plugins

• Create new version.x branch from last commit.
• All plugin changes that remove SSL settings should be in a new major release
• Mark old SSL settings as obsolete
• Add details of change to the 9.0 breaking changes documentation in core.
• 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

Tasks

Tasks

Preview Give feedback

1. Remove deprecated SSL settings from Logstash core #16652
   breaking change deprecation enhancement status:needs-triage v9.0.0 +5
   
2. Remove deprecated SSL settings from Elasticsearch input plugin logstash-plugins/logstash-input-elasticsearch#210
   breaking change status:needs-triage v9.0 +3
   
3. Remove deprecated SSL settings from elasticsearch filter logstash-plugins/logstash-filter-elasticsearch#179
   breaking change v9.0 +2
   
4. Remove deprecated SSL settings from Elasticsearch output logstash-plugins/logstash-output-elasticsearch#1190
   breaking change v9.0 +2
   
5. Remove deprecated SSL settings from Beats/Elastic_agent input logstash-plugins/logstash-input-beats#506
   breaking change v9.0 +2
   
6. Remove deprecated SSL settings from TCP output logstash-plugins/logstash-output-tcp#56
   breaking change v9.0 +2
   
7. Remove deprecated SSL settings for TCP input logstash-plugins/logstash-input-tcp#225
   breaking change v9.0 +2
   
8. Remove deprecated SSL settings from HTTP input logstash-plugins/logstash-input-http#181
   breaking change status:work-in-progress v9.0 +3
   
9. Remove deprecated SSL settings from http filter logstash-plugins/logstash-filter-http#53
   breaking change v9.0 +2
   
10. Remove deprecated SSL settings from HTTP poller input logstash-plugins/logstash-input-http_poller#147
    breaking change v9.0 +2
    
11. Remove deprecated SSL settings for HTTP output logstash-plugins/logstash-output-http#145
    breaking change v9.0 +2
    
12. Remove deprecated SSL settings from serverless forwarder plugin logstash-plugins/logstash-input-elastic_serverless_forwarder#9
    breaking change v9.0 +2
    
13. Add breaking change documentation around deprecated SSL settings removal #16653
    docs status:needs-triage v9.0.0 +3