docs: explain how to use insecure registries with Docker (#23642)

The documentation for the `SSL` option for the Docker driver is
misleading inasmuch as it's both deprecated and non-functional in current
versions of Docker. Remove this option from the docs and add a section
explaining how to use insecure registries.

Fixes: https://github.com/hashicorp/nomad/issues/23616

website/content/docs/drivers/docker.mdx

@@ -324,9 +324,6 @@ The `docker` driver supports the following configuration in the job spec. Only
   }
   ```
 
-- `SSL` - (Optional) If this is set to true, Nomad uses SSL to talk to the
-  repository. The default value is `true`. **Deprecated as of 0.5.3**
-
 - `tty` - (Optional) `true` or `false` (default). Allocate a pseudo-TTY for the
   container.
 
@@ -648,6 +645,21 @@ plugin "docker" {
 !> **Be Careful!** At this time these credentials are stored in Nomad in plain
 text. Secrets management will be added in a later release.
 
+## Insecure Registries
+
+In order to pull images from a registry without TLS, you must configure the
+Docker daemon's `insecure-registries` flag. No additional Nomad client
+configuration is required. You should only allow insecure registries for
+registries running locally on the client or when the communication to the
+registry is otherwise encrypted. List the `insecure-registries` flag in the
+`dockerd` [configuration file](https://docs.docker.com/config/daemon/).
+
+```json
+{
+  "insecure-registries": ["example.local:5000"]
+}
+```
+
 ## Networking
 
 Docker supports a variety of networking configurations, including using host