Implement website redesign

Current design of the Knative website (https://knative.dev/) does not look modern. [Knative UX working group](https://github.com/knative/ux/) has prepared a [new design](https://github.com/knative/ux/blob/main/designs/Website_V1.md) for the website. We would like to get this design implemented in the website.

Notes:
- The repository to work on is https://github.com/knative/docs. The website (knative.dev) is built from that repository.
- There isn't any need for doing any design work. The design is already there (see description above) and it just need to be implemented.
- The Knative documentation website is built using [Material for MkDocs](https://squidfunk.github.io/mkdocs-material/).
- This work goes hand-to-hand with https://github.com/knative/ux/issues/135
- We also want to ensure with this implementation that the figures in the website include alt text descriptions. We are not looking for full WCAG compliance though.

If you would like to participate in the mentorship and if you're eligible, I would not just start with the task directly.

Maybe start exploring how the website works, build it locally, etc.

We will select the mentee based on:
- Proposal: we want the mentee to provide us a plan
- Interaction: we would prefer seeing some interaction from mentee with the community and mentors
- Profile: has the mentee got the required skills? Anything we can see on GitHub?

We will ask you to to apply with a document on LFX platform, when the applications are open.

Read the linked Website_V1.md design and inspect the knative/docs repository, which builds knative.dev with Material for MkDocs. First build the website locally to understand its current structure and entry points. Done means implementing the approved redesign in the website and adding alt text descriptions to its figures.

Written by the indexing model from the issue text.