Describe the bug
Unicode entered as markdown content is rendered as empty rectangles in resulting PDF.

To Reproduce
Steps to reproduce the behavior:

1. Create a report
2. Add visualization, etc.
3. Click "add header"
4. In the header add some emoji or high unicode (I used "🤷‍♂️ m̩ n̩ l̩ 🤦‍♂️") - they show up properly in the "preview"
5. Download the report and see the empty rectangles (see screen shot)

Expected behavior
Character render properly as in preview

Plugins
All OpenSearch plugins

Screenshots

Host/Environment (please complete the following information):

• OS: MacOs
• Version Chrome / 90.0.4430.212 (Official Build) (x86_64)
• OpenSearch 1.0-RC1