Fix line endings and add .editorconfig

https://eaflood.atlassian.net/browse/WATER-4729

When working on updating the environment to Node v22 we encountered an error with the `entrypoint.sh`. Docker compose couldn't find the file when rebuilding the new image.

Huh?

We know! Countless numbers of us have built this environment successfully, but the error was there plain and clear. Perhaps its a change in docker compose?

Anyway, miraculously one of the team tracked it down to the file having a mix of `LF` and `CRLF` line endings. Once they updated the line endings in the file to always be `LF`, docker compose succeeded in building the image.

So, this change corrects all files with mixed line endings. We then add a [.editorconfig](https://editorconfig.org/) file to the repo. We did this to [water-abstraction-system](DEFRA/water-abstraction-system#960) as part of helping to ensure consistency in our code and the same applies here.