Upgrade to Gatsby v4

[kmjennison]

• Check sitemap
• Check robots.txt
• Check metadata on pages
• Check style rendering live on dev -- TODO: needs fixes
• Verify images behave as they currently do
• Verify E2E tests pass

[codecov]

Codecov Report

Merging #266 (4a1068f) into master (e8fb098) will increase coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #266      +/-   ##
==========================================
+ Coverage   78.88%   79.17%   +0.29%     
==========================================
  Files          77       77              
  Lines        1378     1378              
  Branches      256      256              
==========================================
+ Hits         1087     1091       +4     
+ Misses        275      271       -4     
  Partials       16       16              

Impacted Files	Coverage Δ
src/components/MoneyRaised.js	95.23% <0.00%> (+9.52%)	⬆️

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[kmjennison]

May need to also update MUI. Apparently gatsby-plugin-material-ui v4 requires MUI v5 but the plugin's v3 requires Gatsby 3:
hupe1980/gatsby-plugin-material-ui#83

[kmjennison]

Closing for a branch that also upgrades MUI.