manual: conversion of all HTML manual pages to markdown

[neteler]

Test submission of conversion of all HTML manual pages to markdown using the pandoc based converter script (see #4620). Submitted without pre-commit to not be blocked.

For figure code conversion issues, see #4864

[wenzeslaus]

Current state of conversion:

• doc: Add Markdown files #5057 does the adding of files now with the two-commit rename strategy from docs: script to convert HTML manual pages to markdown #4620#issuecomment-2465555707, so the actual Markdown update will be file modification.
• docs: HTML to Markdown lua filters #5054 and doc: Add Markdown files #5057 modify filters so that the CI does not fail. docs: HTML to Markdown lua filters #5054 improves the Markdown itself to pass some of the tests.

[neteler]

@wenzeslaus shall this PR be closed in favor of #5057?