Doc: Update plugin headers to reflect Elastic styles

[karenzone]

The content that appears at the beginning of each of our 200+ plugins comes from plugin headers. Employees and contributors see the outdated standards and take them as the source of truth, perpetuating use of old standards.

Update plugin headers to reflect Elastic standards

Logstash Reference (LSR) header and common files (#16277)

• https://github.com/elastic/logstash/blob/main/docs/include/plugin_header.asciidoc
• https://github.com/elastic/logstash/blob/main/docs/include/plugin_header-integration.asciidoc
• https://github.com/elastic/logstash/blob/main/docs/include/plugin_header-core.asciidoc
• https://github.com/elastic/logstash/blob/main/docs/include/filter.asciidoc
• https://github.com/elastic/logstash/blob/main/docs/include/input.asciidoc
• https://github.com/elastic/logstash/blob/main/docs/include/output.asciidoc

Versioned Plugin Reference (VPR) header and common files (#1687)

• https://github.com/elastic/logstash-docs/blob/versioned_plugin_docs/docs/versioned-plugins/include/6.x/plugin_header.asciidoc
• https://github.com/elastic/logstash-docs/blob/versioned_plugin_docs/docs/versioned-plugins/include/6.x/plugin_header-integration.asciidoc
• https://github.com/elastic/logstash-docs/blob/versioned_plugin_docs/docs/versioned-plugins/include/6.x/filter.asciidoc
• https://github.com/elastic/logstash-docs/blob/versioned_plugin_docs/docs/versioned-plugins/include/6.x/input.asciidoc
• https://github.com/elastic/logstash-docs/blob/versioned_plugin_docs/docs/versioned-plugins/include/6.x/output.asciidoc

Note that there will continue to be some inconsistency between boilerplate text and regular content for a while longer, but we'll be heading in the right direction instead of going backwards.