Use /welcome page instead of /dashboard page when launching a new instance and replace the Dashboard page with the contents of the Welcome page

[anna-geller]

Describe the issue

Currently, when launching a new fresh instance, you will see this page:

We actually wanted to show the /welcome page instead:

Those are almost identical but the one from the Welcome page is better

Ideally, we should always show the video instead of the artwork:

Environment

• Kestra Version:
• Operating System (OS/Docker/Kubernetes):
• Java Version (if you don't run kestra in Docker):