Handle default values from providers' schemas in codegen and codecs

[prolativ]

Inside definitions of providers' schemas elements of properties sections (in definitions of types and resources) as well as inputProperties (for resources only) default values can be specified. These should be taken into account in codegen and in codecs so that users don't have to specify them explicitly and (de-/en-)coding doesn't fail when a property with a default value is missing

[pawelprazak]

I think we might already have this, but needs to make sure we cover all the cases.