Create a `.env` file for every release

Whenever we make a release, we should upload a `.env` file as github artifact that contains a dump of all the environment variables.

- when we run `run_demo.sh` in the integration tests, we take the opportunity to extract the environment variables from `diracx` pod, and we store that in an `.env` file
- this `.env` file is attached only when we make a new release as an artifact
- ⚠️ need to make sure there is no sensitive data uploaded
- this should not be part of `run_demo.sh` because we don't want an end user getting this `.env` file by default
- probably we should add the `.env` file in `.gitignore`

## DoD

- [ ] `.env` file is produced and attached to the release on gh and does not contain any sensitive information