Enrich logs with metadata

### Proposal

Nomad logs which are placed inside the `allocs` directory capture the application logs from `stdout/stderr` directly. There are ways to get metadata using the `docker` driver, by using `logging.config.labels` property, thanks to https://github.com/hashicorp/nomad/pull/9885 which was merged recently. However, I am not sure if there's a way to get this metadata for other task drivers and enrich the logs in the same way. Currently Nomad is basically outsourcing the job of enriching the logs to Docker driver's capabilities. Does it make sense for Nomad to have this feature built in?

### Use-cases

Can get logs with additional context like Job ID, Name, Namespace etc for all jobs started with any task execution driver.

Start by reviewing the Docker driver's logging.config.labels behavior introduced by PR 9885 and how Nomad writes stdout/stderr logs under the allocs directory. Compare that path with other task drivers and document a concrete cross-driver metadata design. Done requires an agreed implementation scope or an explicit feasibility conclusion.

Written by the indexing model from the issue text.