Update registry config options

[miminar]

Update mandatory config options of registry's config file.

This reflects changes brought by openshift/origin#8938

What else need to be documented (not necessarily in this PR):

• introduce manifest schema v2
• make a table of supported configurations of registry version vs docker
  version vs manifest schema version
• document known issues when deployment or build fails due to pulling of
  manifest schema v2 with docker <1.10
• explain when it is (un)safe to accept manifest schema v2

[miminar]

/cc @legionus, @soltysh for technical review

[legionus]

Maybe we can add a short explanation of this ?

This will help to avoid incompatibilities when using clients docker < 1.10 and docker 1.10 and above at the same time.

[miminar]

@soltysh @legionus thanks for the review. I hope I didn't overdo it with verbosity now. Please check it out again.

[legionus]

LGTM

[soltysh]

s/registriy/registry

[soltysh]

Nits, overall LGTM. Thank you!

[miminar]

Addressed. Thank you all.

/cc @ahardin-rh for making this pleasant to the eye.

[ahardin-rh]

@miminar always a pleasure! can you please cross-check my labels and milestone before I merge? thanks!

[miminar]

@ahardin-rh looks good 👍

[ahardin-rh]

[rev_history]
|xref:../install_config/install/docker_registry.adoc#install-config-install-docker-registry[Installing -> Deploying a Docker Registry]
|Updated mandatory configuration options for the registry's configuration file.
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