shell.additional-properties shouldn't be exposed

[snicoll]

If we had a @ConfigurationProperty(ignore=true) then we could flag the additionalProperties field of ShellProperties as it exposes something that we can't bind from simple values.

[philwebb]

I'm not keen to add another annotation (at least not for 1.2)

[snicoll]

If you have another idea I am all ears. Do not forget we are publishing wrong properties in the meta-data now