Design revisions for the /demo/cody page

[iskyOS]

Hi team,

We'd like to update the /demo/cody page. This is similar to this request: #6869.

Since this expands on the previous request, that prior PR can either be closed or used as a starting point for this work.

We would like to do several things on this page:

• Add a video at the top of the page, replacing the HubSpot form that is currently there.
• In the section below the video, remove the product GIF, and raise the section below it (since the GIF will no longer take up space).
• Update the "Sourcegraph powered context" section at the bottom of the page to match the new section that was just added to sourcegraph.com/cody

Figma file with the design: https://www.figma.com/file/Z0vlvOLnDdvJ1PjRpeeCOU/Cody-demo-page-(for-ads)?type=design&node-id=13-949&mode=dev

For the video, instead of embedding it with youtube, we would like to use a native video player with our own hosted files. A video player component already exists in the About codebase which we can use. Please also add a splash screen that shows before the video is played.

Video file: https://storage.googleapis.com/sourcegraph-assets/website/video/Cody%20Page%20April%202024/Cody_the_AI_the_knows_your_codebase.mp4
Splash screen: https://storage.googleapis.com/sourcegraph-assets/website/video/Cody%20Page%20April%202024/Cody_the_AI_the_knows_your_codebase_SplashScreen.webp

[gitstart-app]

Here is the GitStart Ticket for this issue: https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6915