TUS `Upload-Expires` header has wrong format

[individual-it]

Describe the bug

The TUS upload protocol in opencloud implements the expiration extension.

The Upload-Expires response header indicates the time after which the unfinished upload expires.

The value of the Upload-Expires header MUST be in RFC 9110 datetime format.

But opencloud returns a UNIX timestamp

Steps to reproduce

1. create a TUS resource with something like: curl -vk -XPOST 'https://cloud.opencloud.test/remote.php/dav/spaces/7b9d4f7b-2023-4104-a7b0-86c9403d48bf$f4c3d0a5-4c59-4734-97c6-453b11f2752d' -uadmin:admin -H"Tus-Resumable: 1.0.0" -H"Upload-Length: 10" -H"Upload-Metadata: filename ZmlsZS50eHQ=" -H"Content-Type: application/offset+octet-stream" (make sure to send the Content-Type header, otherwise the upload-expires header will not be returned at all, that's an other bug)
2. check the response headers

alternatively:

1. create a TUS resource
2. send a PATCH request to the new resource to upload data
3. check the response headers

Expected behavior

The value of the Upload-Expires header MUST be in RFC 9110 datetime format.

Actual behavior

opencloud returns a UNIX timestamp

Setup

docker compose from devtools/deployments/opencloud_full with additional PROXY_ENABLE_BASIC_AUTH=true