Documentation enhancements

Making metadata:
- more consistent
- more specific (fixed copy pasting)
- refine coverage

Insecure information cleanup

Removing no longer used files:
- mkdocs is gone
- the registry diagram is not used, and is a bit silly :)

Minor fixes

Fixing links

Recipes:
- harmonized code sections style to the rest of the docs
- harmonized recipe "style"
- listing new recipes

Enhance deploying

Signed-off-by: Olivier Gambier <olivier@docker.com>

docs/help.md

@@ -2,7 +2,7 @@
 +++
 title = "Getting help"
 description = "Getting help with the Registry"
-keywords = ["registry, service, images,  repository, help"]
+keywords = ["registry, on-prem, images, tags, repository, distribution, help, 101, TL;DR"]
 [menu.main]
 parent="smn_registry"
 weight=9