Optimize items of the workflow rules array (#1350)
Optimize items of the workflow rules array (#1350)

* Instead of defining the properties of a rule on the top level of the items entry define a whole object (compare https://json-schema.org/learn/miscellaneous-examples.html for the definition of "An array of objects")
* Added `additionalProperties` (only the `if` and the `when` properties are accepted https://docs.gitlab.com/ee/ci/yaml/#workflowrules, additional added properties lead to a yml validation error "workflow:rules:rule config contains unknown keys: xyz")
schemastore/schemastore,schemastore/schemastore