Fix datetime-local field for workflow config

[Arnei]

Fixes #1613

datetime-local fields in workflow config panels would not render, this patch fixes that.
It also fixes a bug where the specified value for the field would be ignored.

How to test this

A workflow config panel can be found for example in the create event dialog.

You'll need to be able to change workflow definitions in the Opencast backend. For example, you could add the following to the configuration_panel_json of the schedule-and-upload workflow.

      {
        "type": "datetime-local",
        "name": "MyDate",
        "label": "This is a date",
        "value": "2026-07-01T12:12:12"
      }

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/admin-interface:pr-1616

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/admin-interface:pr-1616

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.