Improve the Skaffold home page

Unlike the [Skaffold marketing page](https://cloud.google.com/skaffold), this home page does not immediately make it clear that Skaffold’s value proposition includes continuous development, integration, and delivery. We should consider a simple redesign:
* Center the introduction and CTAs, eliminating the outdated (and a11y-unfriendly) terminal GIF.
* Include a basic tile for each component of Skaffold’s value proposition (e.g., [kubernetes.io](https://kubernetes.io/), [kustomize.io](https://kustomize.io/)). With the space saved from consolidating the title content, this should appear above the fold on desktop.
* The Get Started button links to the [Quickstart page](https://skaffold.dev/docs/quickstart). Consider making the Cloud Shell tutorial more discoverable by including the button above the standalone quickstart rather than in its own tab.