Consider replacing the `dotenv` package

In #593, with the major update, they added a new console.log message that prints some ads at the start of the app. I removed it by passing `{quiet: true}` to the config call. But looking at the conversation inside the dotenv repo, I can't say that I would like to use this package anymore. So it would be great to find an alternative and switch to it.

It looks like node has `util.parseEnv` API now but [it's still in active development](https://nodejs.org/api/util.html#utilparseenvcontent). I would like to use it once it becomes stable. It also looks like node supports `node --env-file=.env`, but I don't know if that's a drop-in replacement to dotenv or not yet.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-987)

Start by reviewing the current dotenv config call and comparing Node's util.parseEnv and node --env-file options for compatibility. Done means choosing a supported alternative and confirming that the server's environment loading behavior is preserved without the unwanted dotenv console output.

Written by the indexing model from the issue text.