fix(validation): respect `allowUnknown` route property

[sommestad]

This ensures it is possible to allow unknown properties in request bodies (Postel’s Law), by respecting the x-hapi-options option.

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Discussion

In general, one could consider making allowUnknown: true the default behavior, but I guess that would be considered a breaking change.

Some notes from the thought processes around this change:

• The server wide route option (where this could be set) is apparently not respected by hapi-openapi (probably because validation is overwritten?). Otherwise, that would've been a nice way to avoid this custom property.
• Just providing the validation option does not seem to cut it, since options.validator is overwritten. Avoiding overwriting the provided option (options.validate = Object.assign({}, v.validate, options.validate); did not solve the problem. Hence, I decided to make it an explicit option that trickled down the creation of the validator.
• I decided not to strip the unknown properties, because it's a different property in Hapi (and not necessarily wanted just because unknowns are allowed).

If there's a better way to solve this, I'm all ears, but this was fairly straightforward and did solve the issue.

[tlivings]

Build seems to be failing.

[sommestad]

@tlivings Sorry, had accidentally removed options.validate = v.validate;. Builds successfully now.

[sommestad]

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