Feature Request: switch code from altair-saver to vlconvert

[vevetron]

Where does your feature apply?

altair-saver is now deprecated.

altair-viz/altair_saver#102 - altair-saver is likely no-more, vl-convert is the new way.

Find relevant code that depends on altair-saver and start using vl-convert.

Select from the below, and be sure to affix the appropriate label to this issue (e.g. dataset, jupyterhub, metabase, analysis.calitp.org)

• JupyterHub

Is your feature request related to a problem? Please describe.
It will soon be difficult to maintain altair-saver

Describe the solution you'd like

• update calitp-data-analysis with vlconvert
• Investigate anywhere altair-saver is used and make sure it can use the new package