feat: Update Dockerfile ENV instructions to use `=` instead of whitespace as the key value separator

[alessfg]

Proposed changes

Update the various Dockerfile ENV instructions to use the new format (using = as the key value separator instead of a whitespace) per the latest docs (https://docs.docker.com/reference/dockerfile/#env).

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• [x] I have read the CONTRIBUTING document
• [x] I have run ./update.sh and ensured all entrypoint/Dockerfile template changes have been applied to the relevant image entrypoint scripts & Dockerfiles
• [x] If applicable, I have added tests that prove my fix is effective or that my feature works
• [x] If applicable, I have checked that any relevant tests pass after adding my changes
• [x] I have updated any relevant documentation