Hub: use new artwork

[flavio]

We should update the policy hub website to use the new artwork we got.

Acceptance criteria

• The new logo is used: https://github.com/rancher/project-assets/tree/master/logos
• The new color palette is used: https://github.com/rancher/project-assets/blob/master/colors/colors.md#kubewarden

[flavio]

@ncounter this is something where we need your help :pleading_face:

[ncounter]

@flavio booked. Any due date?

PS: I updated the issue description with the color palette link :wink:

[flavio]

We should get it done by the end of this month. KubeCon begins on the 4th of May

[ncounter]

Addressed in https://github.com/kubewarden/policy-hub/commit/e2c92cc54c71c5e05f436c63e4217ed8ce239164