docs/usecase: add ssl reverse proxy usecase

- Add SSL reverse proxy case setup scripts
- Add SSL reverse proxy case guide
- Support for loopback and interfaces

Signed-off-by: Liangxing Wang <liangxing.wang@arm.com>
Signed-off-by: Yefeng Lin <yefeng.lin@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>
Reviewed-by: Lijian Zhang <lijian.zhang@arm.com>

Change-Id: I273d609acfb9602a21f98a143043f17d1a486f38