Mardown is not converted for h4 to h6

[virgile-dev]

Bug Report

Problematic behavior
When I type #### title
It does not convert to a title 4 automatically like it should
Also in the summary titles above level 3 do not display

Expected behavior/code
A #### tiIte should convert to a title 4 automatically
Titles of all levels should display in the summary

Environment

• Docs version: 3.8
• Instance url: docs.numerique.gouv.fr

Possible Solution

Additional context/Screenshots
Linked to #1146

[AntoLC]

A #### tiIte should convert to a title 4 automatically

Made here: #1375

[AntoLC]

Titles of all levels should display in the summary

Excluded by purpose, as talk with @rl-83:

• ✨(frontend) exclude h4-h6 headings from table of contents #1441
• Ignore h4 to h6 headers in document outline (or properly indent them) #1435