Multiple accessibility issues in the new (and existing) Gitpod interface

Bug description

There are a few accessibility issues in the new Gitpod interface, some examples:

• Not enough color contrast between text and background
• Not possible to tab through all the items using a keyboard
• Some items missing a clear focus border
• Some images miss alternative text
• Does not respect prefers-reduced-motion
• Almost no use of Aria attributes
• Lack of semantic HTML usage

Steps to reproduce

Open https://main.staging.gitpod-dev.com

• Try navigating through items with keyboard
• Open devtools, inspect images, and see alternative text is missing
• Start a project, the jumping G logo would jump even when prefers-reduced-motion is set in the user's browser.

Expected behavior

Make Gitpod a fully accessible experience

Example repository

https://github.com/gitpod-io/gitpod

I'll be happy to help identify more accessibility issues, and help resolve them as well :)

Start by opening https://main.staging.gitpod-dev.com and reproducing the listed keyboard, focus, image alternative-text, and reduced-motion problems with browser developer tools. The issue provides no file or test entry point; done would require addressing the identified accessibility problems across the interface and verifying the listed behaviors again.