refactor: map binary params to io.Reader in Go client

[dschmidt]

Adds --type-mappings=binary=io.Reader,file=io.Reader,File=io.Reader to the Go generator invocation so binary request/response bodies (e.g. UpdateOwnUserPhotoPut, GetOwnUserPhoto) are emitted as io.Reader instead of *os.File.

*os.File satisfies io.Reader, so existing callers compile unchanged. The runtime setBody path in the generated client already prefers io.Reader over *os.File, so behavior is identical at the wire.

The download path relies on the *io.Reader branch added to the shared decode helper in OpenAPITools/openapi-generator#23789, released in openapi-generator 7.23.0. The generator_image pin in .woodpecker/build-go.yaml is bumped from v7.13.0 to v7.23.0 accordingly, so GetOwnUserPhoto / GetUserPhoto decode into io.Reader instead of returning "undefined response type".

[dschmidt]

Stumbled upon this when I reviewed opencloud-eu/opencloud#2704.

If we're going for the event based approach I suggested (and which the author already implemented), we don't need this anymore. But it's still more correct and more flexible and more idiomatic. I strongly suggest to merge this fix anyhow :)

[dschmidt]

If you prefer I can send a preliminary PR that just bumps the openapi-generator - then it becomes more obvious what is changed by the flags I'm introducing in this PR