Rename `deno --env` to `deno --env-file`

[birkskyum]

I'd suggest renaming --env to --env-file in Deno 2 for the following two reasons:

1. It's more obvious that it'll take a path to an .env file and not i.e. a ENV_VARIABLE=VALUE pair, or like jest --env takes an environment such as jsdom.
2. It's called --env-file in both node and bun, and having it be the same in Deno reduces cognitive overhead, and mitigate migration issues.