Improve Editor UI and fix bugs

[ybiquitous]

Which issue, if any, is this issue related to?

None.

Is there anything in the PR that needs further explanation?

• Show a warning indicator in the editor UI; internally using Monaco Editor's model markers See https://microsoft.github.io/monaco-editor/playground.html#extending-language-services-model-markers-example
• Use metadata for a rule doc link
• Fix an invalid link for syntax error
• Update the monaco-editor package and add it to dependencies explicitly so that we can easily see it as outdated

[ybiquitous]

Thanks for the review!