Add Option to disable validation

[Stefano Coletta]

When using a private repo, the validation cannot succeed because it lacks authentication info.

This is also true if the repo is not accessible from the internet.

https://online.swagger.io/validator?url=<myurl>

<myurl> will be inaccessible from swagger.io

I propose to add an option (on/off) to the Confluence macro to choose if you want the validation to be done or not.

This way I can avoid this INVALID image on the bottom of the page.

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