Add "failOnError" option

[dragankoz]

When the plugin fails to retrieve the openapi file fromt the server, it should error stop the maven build process.
Currently an error is emitted but the maven process continues.

e.g. [ERROR] An error has occured: Response code 401

[codespearhead]

I'm afraid it's not clear what you're reporting. We need an MRE.

[timbuethe]

@dragankoz feel free to "upvote" this MR :-)
#60