Expose submitted job/layer environment variables via the OpenCue API

**Is your feature request related to a problem? Please describe.**

First of all, thank you for maintaining OpenCue.

When working with existing jobs, we noticed that environment variables set at submit time (for example via job.set_env(key, value, pre=True)) are persisted in the database but are not currently accessible through the OpenCue API after submission.

This makes it a bit difficult for us to inspect or reproduce jobs when troubleshooting or re-submitting them.

**Describe the solution you'd like**

If possible, we would love to have a way to retrieve environment variables associated with a submitted job and/or layer through the OpenCue API.

Being able to access job-level and layer-level environment variables would greatly help with debugging, inspection, and reproducibility in pipeline automation.

**Additional context**

This topic came up in a discussion on the Slack OpenCue forum, where it was mentioned that environment variables are already stored in the database but are not currently exposed via the API. (https://academysoftwarefdn.slack.com/archives/CMFPXV39Q/p1768418868091959?thread_ts=1768265853.590659&cid=CMFPXV39Q)