Add ability to show warning text from Auspice JSON

[victorlin]

from Slack

Render a new JSON entry for warnings (e.g. meta.warning) along the lines of @trvrb's mock-up:

Related issues

• export: Add warning text to output JSON and schema augur#1722

[victorlin]

Noting that this is somewhat clashing with the existing warning notification framework, but arguably serves a different purpose. The proposed warnings are more about the underlying data than potential programming issues, and meant to persist on the page rather than disappear after a few seconds.

[victorlin]

A PR is out for review, but open to suggestions on details such as:

• Key name – currently meta.warning
• Placement – currently between byline and sample summary
• Contents – currently supporting Markdown format
• Design – currently black text, warning icon, some padding, yellow background, and a more saturated left border.