Visualisation of model results (interactive + static)

[jameshadfield]

This PR introduces a standalone react app for visualising the model outputs which are generated by this repo. The visualisations themselves are based on these existing notebooks.

Current status

Visualisations are in-browser static d3 plots, which are responsive to different browser sizes. They only exist for three model outputs, each with a single visualisation style. These can be run locally (instructions in the ./viz/README.md`).

A script generates static png images of these plots, which can be rendered in a markdown document similar to the above notebooks. Here is a preview of that markdown:

There's plenty of fun stuff we can do with the interactive visualisation (which I'm looking forward to), however the immediate focus should be on automating the deployment of these.

Next steps

• Make the model-output JSONs publicly available, and adapt the app to fetch these (rather than reading them from disk). There should also be a /latest.json (or similar) JSON which the app can fetch by default.
• Use this react element within nextstrain.org, or similar. There's lots of ways to do this, and I'm not sure which is the best...
• Share the statically generated versions through nextstrain.org or GitHub. Again, plenty of ways to do this and I'm not sure which is the best.
• Regenerate the static images each time a new model run is available (the interactive version could just point to /latest.json)

[joverlee521]

Did a test run of the new GH workflow to generate static figures of model results with:

gh workflow run generate-static-model-viz.yaml --field trial_name=config-latest-results --ref viz

The test run uploaded the figures to:

• s3://nextstrain-data/files/workflows/forecasts-ncov/gisaid//trial/config-latest-results/nextstrain_clades/global/renewal/frequenciesPanel.png
• s3://nextstrain-data/files/workflows/forecasts-ncov/gisaid//trial/config-latest-results/nextstrain_clades/global/renewal/legend.png
• s3://nextstrain-data/files/workflows/forecasts-ncov/gisaid//trial/config-latest-results/nextstrain_clades/global/renewal/rtPanel.png
• s3://nextstrain-data/files/workflows/forecasts-ncov/gisaid//trial/config-latest-results/nextstrain_clades/global/renewal/smoothedIncidencePanel.png

[jameshadfield]

I'm planning on merging this PR today / tomorrow, as part of the following to-do's to get the model viz deployed on nextstrain.org:

• [ ] This PR
• [ ] Update, retest & merge https://github.com/nextstrain/nextstrain.org/pull/641
• [ ] Modify main model pipeline so that the GitHub action generate-static-model-viz (created in this PR) is automatically triggered after model results are uploaded to S3
• [ ] Add intro text to static pages https://github.com/nextstrain/nextstrain.org/pull/580
• [ ] Use static images created by generate-static-model-viz in https://github.com/nextstrain/nextstrain.org/pull/580
• [ ] merge https://github.com/nextstrain/nextstrain.org/pull/580