[INFRA] Review the infrastructure of the demo

[tbouffard]

In version 0.3.0, we introduced an home page and a new demo for overlays.
We already see duplication, we are using vanilla TypeScript, vanilla CSS and it is going to be worse if we continue like this for new demo.

We have already some needs that are common to all demos

• button to choose a local diagram
• common header
• common design
• provide sample diagrams in the demo? could be taken from the files used as fixtures of tests

Additional context

Decide

• if we create a single page application
• if we use framework like Vue/Svelte
• how we handle the design: use a framework like in bpmn-visualization demo with tailwindcss for example?
• introduce components for shared elements or reuse existing ones. For instance, button for local diagram load.
• ....

[UPDATE 2023-10-10] We should also consider storybook.js.org/ that will help to easily deal with options of the features we want to demo as it provides a way to configure them with "arguments". Users can then play with the options directly from the UI.
We could also create component dedicated for the demo (for instance diagram navigation buttons) using a framework supported by storybook (Angular, React, ...)
We recently did some work with storybook in

• chore: migrate to storybook v7 maxGraph/maxGraph#230
• feat(poc): put the examples in storybook bpmn-visualization-examples#548