nixos/docker-registry: cleanup module definition & enhance testcase

The following changes have been applied:

- the property `http.headers.X-Content-Type-Options` must a list of
  strings rather than a serialized list
- instead of `/etc/docker/registry/config.yml` the configuration will be
  written with `pkgs.writeText` and the store path will be used to run
  the registry. This reduces the risk of possible impurities by relying
  on the Nix store only.
- cleaned up the property paths to easy readability and reduce the
  verbosity.
- enhanced the testcase to ensure that digests can be deleted as well
- the `services.docker-registry.extraConfig` object will be merged with
  `registryConfig`

/cc @ironpinguin

1 files changed, 7 insertions, 0 deletions

diff --git a/nixos/doc/manual/release-notes/rl-1809.xml b/nixos/doc/manual/release-notes/rl-1809.xml
index 62f1b769463..5ff5caaf255 100644
--- a/nixos/doc/manual/release-notes/rl-1809.xml
+++ b/nixos/doc/manual/release-notes/rl-1809.xml
@@ -77,6 +77,13 @@ following incompatible changes:</para>
       accepted by the nc command.
     </para>
   </listitem>
+  <listitem>
+    <para>
+      The <varname>services.docker-registry.extraConfig</varname> object doesn't contain
+      environment variables anymore. Instead it needs to provide an object structure
+      that can be mapped onto the YAML configuration defined in <link xlink:href="https://github.com/docker/distribution/blob/v2.6.2/docs/configuration.md">the <varname>docker/distribution</varname> docs</link>.
+    </para>
+  </listitem>
 </itemizedlist>
 
 </section>