Have vs code markdownlint extension use config file

[thompson-tomo]

Changes

This cleans up the vscode settings to use the markdownlint config file and recomended that users install the extension.

Also remove un-used settings.

For non-trivial changes, follow the change proposal process.

• Related issues #
• Related OTEP(s) #
• Links to the prototypes (when adding or changing features)
• CHANGELOG.md file updated for non-trivial changes
• spec-compliance-matrix.md updated if necessary

[trask]

I like the idea, but looks like this extension is based on markdownlint-cli2, and so flags a lot of things that our existing configuration (based on older version) doesn't

I'd suggest updating the repo to markdownlint-cli2 first and updating configuration to match current repo practices and then come back to this

[thompson-tomo]

I took a look at this and it appears that the first issue is that markdownlint-cli has not been updated.

It is however now pending in the Dashboard #4507

The marketplace listing mentions it supports both. I have also confirmed that is the case. I will submit seperate PR to update rules which will enable update to be merged.

[thompson-tomo]

Pr which applies the latest linting rules is ready as #4756 in that pr when I disabled a rule the violations updated in vs code.