Refactor documentation to consider single Helm chart

[jvanz]

We have a change in progress to merge our 3 Kubewarden admissions controller helm charts (kubewarden-defaults, kubewarden-controller and kubewarden-crds) into a single one. This was defined in the RFC0026.

This means that we need to adjust our documentation to consider this new way to install, upgrade and uninstall Kubewarden admission controller stack.

Acceptance criteria

• Update the quick start to show how to install Kubewarden admission controller using the single helm chart
• Look for all helm commands installing or upgrade Kubewarden admission controller and update them
• Take a look in the documentation overall looking for places where the text should be updated to be adapted to the new Helm chart

[flavio]

We definitely have to update the quickstart and the gitops instructions