[🐛/🚀 site]: internal page anchors are not generated automatically

[ala-n]

As an ESL documentation consumer, I want to have in-page links working.

Page(s)
https://esl-ui.com/core/esl-event-listener/ (v4.2.0)

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As an ESL documentation writer, I want to have them generated automatically.

The proposed scope of the update and notes:

1. Integrate the postprocessing worker to provide stringified and simplified ids for headers with the levels 1-4
   • ignore any characters except numeric and Latin symbols
   • make sure the shortcode insertions in headers work properly
   • consider limiting the id length
2. Consider a separate request to support references by the keyword to be processed automatically
   • Most likely should be limited