How to implement file upload?

[andrashatvani]

Currently there's no example demonstrating the implementation of a file upload. Desired would be one example with both, single and multiple files.

[smyrick]

From the issue #1036

Apollo file uploads are not part of the GraphQL specification and are not supported "out-of-the-box". As per #518 you will have to
configure Jackson object mapper to correctly handle those types (and potentially also configure custom data fetcher to apply the
custom logic - if needed).
There are some examples linked in other related issues #661 (comment) and #518 (comment)