3_Developer_Guides: add new app framework documentation
Starting with `marlin`, the old AppFW has been phased out and replaced
by a new implementation, relying mainly on standard technologies and
software. This commit documents the current state of the new Application
Framework so developers can create compliant applications.
Bug-AGL: SPEC-4236
Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>
Change-Id: I4cf52799426efbc2401b8785aaa57cc925a4968f
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/27166
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>