Fix #71295 Permit command URIs in markdownDescription of extension setting

[gjsjohnmurray]

This PR fixes #71295

To test:

• Clone https://github.com/gjsjohnmurray/vscode-extension-samples/tree/test-vscode-71295
• Open the configuration-sample folder and build and run that sample extension.
• Open the Settings page and search for 71295.

Without this PR it will look like this:

With this PR the word 'here' becomes a hyperlink (command:workbench,view.extensions) that switches to Extensions view.

[gjsjohnmurray]

@roblourens is this your domain?

[roblourens]

Thanks!