Make distroless/base as the base image for the default image,
effectively making the minimal image as the default. Add a new "full"
image variant that corresponds the previous default image. The
"*-minimal" container image tag is provided for backwards compatibility.
The practical user impact of this change is that hook support is limited
to statically linked ELF binaries. Bash or Perl scripts are not
supported by the default image, anymore, but the new "full" image
variant can be used for backwards compatibility.
Introduce two main sections "Deployment" and "Usage" and move "Developer
guide" to the top level, too. In particular, split the huge
deployment-and-usage file into multiple parts under the new main
sections. Move customization guide from "Advanced" to "Usage".
This patch also renames "Advanced" to "Reference" as only that is left
there is reference documentation.
