Using DocumenterVitePress as new documentation site

[VEZY]

See #60.

Also, remember that we can't merge before LuxDL/DocumenterVitepress.jl#38 is fixed. It will add documentation versioning, which is a required feature for me.

To do:

• Add the home page (see docs/src/.vitepress/theme/index.ts + https://github.com/LuxDL/DocumenterVitepress.jl/blob/master/docs/src/index.md)
• Add a favicon + logo (track here: Make a logo and icon #70 ), see: https://github.com/LuxDL/DocumenterVitepress.jl/tree/master/docs/src/assets

[VEZY]

To run it locally, cd into docs, and run:

npm i

It will install all dependencies found in the package.json file.

Then open a julia instance in the docs folder, activate the environment and run:

include("make.jl")

And in another terminal, run:

npm run docs:dev

Then you'll have a site that is served locally.

[VEZY]

The website is here: https://virtualplantlab.github.io/PlantSimEngine.jl/previews/PR69.
Although it builds fine locally, the build on GA is faulty and needs to be checked.

[asinghvi17]

If you're not deploying a custom theme via the Vitepress files, you can remove them + the package.json!

[VEZY]

Thank you for the review @asinghvi17! The website builds nicely locally, but it's not building properly on github pages, do you have any idea why?