Put collectionFormat in one place

[fizruk]

For example, in ParamSchema. This might enable things like:

newtype CSV a = CSV { getCSV :: [a] }

instance ToParamSchema a => ToParamSchema (CSV a) where
  toParamSchema _ = mempty
    & schemaType .~ SwaggerArray
    & schemaCollectionFormat ?~ CollectionFormatCSV
    & schemaItems ?~ SwaggerItemsPrimitive (toParamSchema (Proxy :: Proxy a))

Alternatively we can leave it in Items, changing its meaning to "collection format of these items (always required)". Then CSV example above would look like this:

newtype CSV a = CSV { getCSV :: [a] }

instance ToParamSchema a => ToParamSchema (CSV a) where
  toParamSchema _ = mempty
    & schemaType .~ SwaggerArray
    & schemaItems ?~ SwaggerItemsPrimitive CollectionFormatCSV (toParamSchema (Proxy :: Proxy a))

If there is a solution where we can put collection format entirely out of schema — that would be preferable, since ParamSchema is contained in Schema and collection format does not make sense for the latter.