[FEAT] Add an example of a project using Preact

[tbouffard]

See https://preactjs.com/ and https://github.com/preactjs/preact

Contribution guidelines

• first, post a comment to mention you are interested in contributing, then you will be assigned to the issue
• we prefer TypeScript projects
• store it in a sub-folder of the projects directory
• choose use case
  • It can be a basic integration that simply displays the diagram, or use an API as we do in the "projects" showing how to integrate bpmn-visualization with build tools and bundlers.
  • It is perfectly valid to provide a contribution using the framework starter kit.
  • It can include dedicated use cases, as Angular or Vue integrations do.

In any case, please communicate with the maintainers of this repository (with this issue) about what you want to implement (especially the use case) to make sure we're aligned on this.
This will speed up the review and final integration into the examples.