Add openssh-sftp-server when agl-devel is on

Add openssh-sftp-server when agl-devel is on

For simplified development workflows on newer host distros add the sftp server.

Bug-AGL: SPEC-4443
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Change-Id: I580e5d342fb6afb286b00d41b03c98a9b936160f
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/28018
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Marius Vlad <marius.vlad@collabora.com>