Fix: Pass additional color specifications to charts

[mayagbarnes]

Describe your changes

Handles column specification in altair charts by passing header defaults for fonts/colors to both default and streamlit chart themes in CustomTheme.tsx

Before:

After:

GitHub Issue Link (if applicable)

Closes #3343

Testing Plan

• E2E Tests - Snapshot tests added ✅

[willhuang1997]

Would it be sufficient to just add some headers to an already existing test and update that snapshot? Seems unnecessary to create two new tests when we are just adding some properties to customTheme.tsx imo. In addition, it would remove the barley Vega dataset and thus make the test code easier to read.

[mayagbarnes]

Probably, but I haven't been able to simply add headers without disrupting the whole chart config (can't say altair charts are a strong suit I guess). Open to help on how to do so!
Alternatively I can remove the plain bar chart tests to reduce # of tests?

In the meantime going to see if I can import it from vega_datasets instead

[willhuang1997]

Ah yeah removing the plain barcharts sounds like a good idea

[mayagbarnes]

@willhuang1997 Could you give this another look when you have a chance 😃