Allow setting `force_https = true` in `fly.toml`

[schu]

I would like to force http -> https redirects, but as far as I see it's currently not possible to set force_https = true for the generated fly.toml file.

Am I missing something or is this an option that could be exposed to the user? (Personally, I wouldn't mind to hard code force_https = true in FLY_TOML though.)