Add json-schema for pod-specifications.

[floitsch]

Enables completion and validation in editors that support json-schema.

To test, download the schema and add the following property to a pod-specification file:

  "$schema", "file:///path/to/schema"

Once the schema is published, we should then require the $schema (instead of "version": 1), thus identifying the document and its version.

Basically, pod-specifications should then always have:

"$schema": "https://raw.github.com...."

Also note: json-schemas work for yaml files too, as long as the yaml-extension (from Red Hat) is installed. However, they want the schema as comment:

# yaml-language-server: $schema=<URI>

We could make this a requirement for our pod specifications (if written in YAML).

[kasperl]

Looks good to me.