Markdownlint new rule: Custom replacement for MD048 - fenced codeblocks rule with fixer

[MaoShizhong]

Because

Markdownlint's built-in MD048 rule for fenced code block style does not include fix information, so will require manual fixing. It would be more straightforward for us to disable the built-in and use a custom rule to enforce the same style and provide a custom fixer for our fix scripts.

This PR

• Adds a custom version of the MD048 built-in, with fix info
• Adds appropriate test and doc files
• Appends custom rule to markdownlint config custom rules array
• Disables the built-in MD048 rule

Issue

N/A

Additional Information

Discovered through this, TOP006 will need amending to account for ~ code blocks as well. Currently it only recognises ` code blocks, so something like ~~~md will be fixed to ```md instead of ```markdown. This will be handled in a separate PR. Fixed in #27916

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide