Update reference docs. (#5623)
Update reference docs. (#5623)

- Update to latest version of protoc-gen-docs

- Add sorting of debug scopes in pkg/log so that generated docs are consistent.

- Update pkg/collateral to generate description: front-matter instead of overview:
as per the latest changes in istio.github.io

- Update protos to use $description instead of $overview:

- Move template examples from appearing on the template message to appearing on the
package. This ends up giving a better flow in the generated docs.

- Move the location of adapter & template docs into a subdirectory on istio.io for better
organization.

- Document which template each adapter supports.
istio/pkg,istio/pkg,istio/pkg,istio/pkg,istio/pkg