inform users which ENV VARS get set by `wasp deploy fly launch`

it's unclear which (server) ENV VARS are set automatically and which VARS users need to set themselves when deploying via wasp deploy fly launch.

Since Wasp automatically sets the following vars (below) via the deploy command, it would be best if we informed the user about this:

[ ] in the "Deployment" docs
[ ] in the "Env Variable" docs
[ ] in the console after running wasp deploy fly launch

https://github.com/wasp-lang/wasp/blob/main/waspc/packages/deploy/src/providers/fly/setup/setup.ts#L116

const secretsArgs = [
        `JWT_SECRET=${randomString}`,
        // NOTE: Normally these would just be envars, but flyctl
        // doesn't provide a way to set envars that persist to fly.toml.
        'PORT=8080',
        `WASP_WEB_CLIENT_URL=${deploymentInfo.clientUrl}`,
        `WASP_SERVER_URL=${deploymentInfo.serverUrl}`,
    ];

wasp-lang / wasp

inform users which ENV VARS get set by `wasp deploy fly launch` #2055