Describe the feature:
TSVB still uses the EuiCodeEditor component in 2 places:

1. src/plugins/vis_type_timeseries/public/application/components/markdown_editor.js
2. src/plugins/vis_type_timeseries/public/application/components/panel_config/markdown.tsx

These code should be refactored to use Monaco editor instead.

This work must be done for the following reasons:

1. EUI recommendation, see [EuiCodeEditor & EuiCodeBlock] Recommendations and migration guidance eui#3807
2. Bundle optimization. I expect to see minus ~800Kb in async chunks