Add env var for pointing app at lexbox

[myieye]

Fixes #1767

Description

We want LexBox to get as much "real" use as possible, so we plan to point the staging environment at it for fetching the list of LD projects.

As is obvious in the change set, I tested this against lexbox locally and in staging. Referencing db as lf-db was necessary, because both docker networks had a db.

This won't work (at the time of writing), because the LexBox API only supports form-data, which is what Chorus sends. It might be safe to just change lf-classic to do the same, but it feels a bit better supporting both, because 🤷 there might be another service sending json.

Checklist

• I have labeled my PR with: bug, feature, engineering, security fix or testing
• I have performed a self-review of my own code
• I have reviewed the title & description of this PR which I will use as the squashed PR commit message
• I have commented my code, particularly in hard-to-understand areas
• I have enabled auto-merge (optional)

Testing

We'll turn this on in staging, once LexBox supports JSON.

[github-actions]

Unit Test Results

362 tests   362 ✔️  19s ⏱️
  37 suites      0 💤
    1 files        0 ❌

Results for commit 45916ad.