Use the right gif / videos

[RymMichaut]

Description
This improvement addresses the documentation home page.

Expected change
What would be the expected outcome:

Remove the current gifs:

Use the right videos (the one on the Avaiga/taipy Readme) :

[jrobinAV]

I believe we should not just replace the GIF.
I would review the whole page's content to make it more use-case-driven. What are the problems we want to solve? Something more consistent with the new organization of the user man.
For example:

• User interface
• Page design
• Data integration
• Task orchestration
• What if analysis