ci-automation/release: Set up rclone config for mapping into container

[pothos]

The wrong variable was used to set up the mapping of the rclone config
into the rclone container and it wasn't set up in the right function.
Move it into the right function and use the right variable name but also
don't rely on /proc/PID/fd/FD to be mappable into the container but
instead use a regular temp file.

How to use

Cherry pick to the release branch and retag, then rerun the release job 🙃

Testing done

None!

[pothos]

FYI, this was the error:

 Status: Downloaded newer image for rclone/rclone:1.71.1
 docker: Error response from daemon: create ****: "****" includes invalid characters for a local volume name, only "[a-zA-Z0-9][a-zA-Z0-9_.-]" are allowed. If you intended to pass a host directory, use absolute path
 
 Run 'docker run --help' for more information
 Finished with result: exit-code

Which I think comes from the wrong variable which had base64 content passed in, and as it's a secret it got masked with ****

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/19268752860