[docs] update to GA-4

[odow]

This won't fix all of the existing HTML files in gh-pages branch. I'll need to fix that manually.

I've tested that this is all we need to do in SDDP.jl https://github.com/odow/SDDP.jl/pull/723

x-ref https://github.com/JuliaDocs/Documenter.jl/issues/2016

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (868b3d5) 98.27% compared to head (0f46777) 98.27%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3640 +/- ## ======================================= Coverage 98.27% 98.27% ======================================= Files 43 43 Lines 5639 5639 ======================================= Hits 5542 5542 Misses 97 97 ```

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[odow]

Working