[REFACTOR] Add missing favicon in the frontend

[tbouffard]

In v1.0.0, the favicon is missing.
Please ensure that we use the new colors of the website (the examples repository may not use it). See also process-analytics/bpmn-visualization-examples#465

We could use the same file as in the other repositories

• https://github.com/process-analytics/bpmn-visualization-demo-template/blob/v1.0.0/public/logo.svg
• https://github.com/process-analytics/bonita-day-demo-2023/blob/87b5b7858531a02caec7a3ba2b6b5ce599f27c6b/public/logo.svg
• in the bpmn-visualization-examples repository, for example: https://github.com/process-analytics/bpmn-visualization-examples/blob/v0.31.0/examples/favicon.svg