Description

Unbreaks incorrect overwriting of environment by skipping copy of .env.local if .env or .env.local already exist.

Checklist

[x] I have installed pre-commit and installed the hooks with pre-commit install before creating any commits.
[x] I have updated any related tests for code I modified or added new tests where appropriate.
[x] I have manually tested my changes as follows:
- cd frontend
- cp .env.dist .env
- Set NEXT_PUBLIC_BACKEND_URL to anything other than localhost
- cd ../docker
- docker compose -f docker-compose.prod.yml -f docker-compose.yml up
- Make sure the front end requests from the URL you specified in NEXT_PUBLIC_BACKEND_URL as opposed to localhost
[x] I have updated any relevant documentation or created new documentation where appropriate.