copy file to runing nomad task/allocation with cli or api

### Proposal
Hello,

as @jrasell suggested, i asked if there is already a way to do this to [hashicrop discussion](https://discuss.hashicorp.com/t/how-to-copy-file-to-runing-nomad-task-allocation-with-cli-or-api/26106), but unfortunately, there is no way. So im posting it here.
im wondering, when nomad task using volume. i want to transfer file from local or some config deployment to a running nomad job/task. something like `docker cp` to container filesystem or its volume.

thank you.

Start with the linked HashiCorp discussion to understand the existing limitation and the requested behavior. Scope the CLI or API entry point for copying a local or deployment-provided file into a running Nomad task or allocation, and define done as a documented, working equivalent of docker cp for the task filesystem or volume.

Written by the indexing model from the issue text.