Rename PCS_CONFIG_URL in Simulation docker-compose files

[peterfelts]

While working on an RM release @isaac-dasan noticed that the diagnostics service wasn't starting (for RM deployments) because it was looking for an environment variable that was missing. We tracked this down to a merge where the name of the environment variable was changed. Here we'll change the environment variable to be consistent with RM, and I'll update the diagnostics service as well.

Change type

• [x] Bug fix
• [ ] New feature
• [ ] Enhancement
• [ ] Breaking change (breaks backward compatibility)

Checklist:

• [ ] All tests passed
• [ ] The code follows the code style and conventions of this project
• [ ] The change requires a change to the documentation
• [ ] I have updated the documentation accordingly

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This change is