Fix/rte convert bad headings

[andrewleith]

Summary | Résumé

This pull request introduces improvements to the markdown editor's handling of headings. It adds a feature that automatically corrects common markdown heading formatting mistakes, ensuring consistent rendering in the editor.

During markdown conversion, the following 2 things will now happen:

• #heading will be changed to # heading
• #subheading will be changed to # subheading

Test instructions | Instructions pour tester la modification

• Switch to markdown mode
• Enter a heading with the wrong syntax (ie. #Heading or ##Subheading)
• Switch to editor
• Ensure headings convert to h1/h2 as appropriate
• Switch to markdown
• ensure markdown has been fixed (i.e. # Heading or ## Subheading)

[github-actions]

🧪 Review environment

https://gi6wfegqmjeafkcf4qb6i4d2hu0wfbxf.lambda-url.ca-central-1.on.aws/