fix(config): Add sample data visibility env flag

[arhowe00]

Closes #759

Configures the initial visibility state at build time. Can prevent a benign race condition between the default (true) and runtime-fetched (false) settings where delayed state update looks ugly.

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[PaulHax]

lets remove the non working configJson.ts code that trys to configure this

[arhowe00]

lets remove the non working configJson.ts code that trys to configure this

I thought we still wanted the ability to override the .env value with the json configuration file. Do you want the configuration file to still work to enable/disable it?

[PaulHax]

I thought we still wanted the ability to override the .env value with the json configuration file.

I guess I missed that requirment. I don't think that is needed. 2 places to config the same thing? There is an opprotunity to have a negative line count commit, which makes me happy.

[floryst]

I can see the argument for removing the configJson code that handles sample data visibility. Users likely won't care to configure it at runtime, and instead only care about having an app that either shows it (unlikely) or doesn't show it (likely).

Scratch the overriding idea. Let's just remove it entirely from the configJson code.

[floryst]

You'll need to add VITE_SHOW_SAMPLE_DATA to https://github.com/Kitware/VolView/blob/main/.github/workflows/checks.yml in order for the tests to pass.