swctl: added usage condition for entity's extra file

[fgschwan]

Adds possibility to control creation of extra files from entity based on condition. For example this code will deploy given yaml only for demo deployment (DEMO_DEPLOYMENT is entity input variable)

    files:
      - name: "additional-config-for-demo.yaml"
        when: "${DEMO_DEPLOYMENT}"
        content: |
         ...

The condition is fully-evaluated template (just as entity config) and its content is evaluated (strconv.ParseBool) to find whether to create this file ("when" content is parsed to true boolean) or not ("when" content is parsed to false boolean).