image-fixedfunction: rename minimal to fixedfunction

Rename minimal to fixedfunction to reflects the Fixed function device scenario from Apertis Platform Technical Vision.

Add nginx web server with minimal static web content to exercise basic demo function.

Fix python3 in sample development image which depends on packages from development, so install it after adding development repository.

Signed-off-by: Frédéric Danis frederic.danis@collabora.com