[meta] elasticsearch integration plugin

[kares]

The ES plugins: filter, input, output should get merged into one integration plugin.

Pieces to consider while revamping plugins:

• proxy => ... isn't supported by all plugins
• ssl support provide the same basic configuration for all plugin types e.g.
  • filter is missing ssl_certificate_verification
  • input is missing ssl_certificate_verification
• Encountered a retryable error. Will Retry with exponential backoff logstash-plugins/logstash-output-elasticsearch#823
• unified TLS material setup for testing against ES (a discussion)
  • current testing setups will simply expire in a few years, certificates have been copied from plugin to plugin

[rafzei]

@kares Actually property ssl_certificate_verification is missing for input plugin as well.
docs
Error msg:
[ERROR] 2020-08-26 11:02:20.090 [Converge PipelineAction::Create<main>] elasticsearch - Unknown setting 'ssl_certificate_verification' for elasticsearch
I see a few PR for this issue but nobody wants to merge it: here