Templating is weird af in Rocket. Look into 3a541ae for more.
The content-type of the rendering is determined by the extension of the
template name.
But renaming these templates would break building the project for
development because it finds a phony template there. So the trick is to
default the `template_dir` to `args.upload` because it should never
interfere and will be always present.
This also fixes the hax in Dockerfile by making it the default.
Signed-off-by: Gunwant Jain <mail@wantguns.dev>
