XDS server need to easily retrieve the list of SDKs available for now in https://download.automotivelinux.org/AGL/release/ and in https://download.automotivelinux.org/AGL/snapshots/master/

Current implementation (based on a bash script) is not robust at all and not efficient (take approximately 2min). And there is also a problem that some SDKs/builds are not located on the same storage/server (eg. mirror servers for https://mirrors.edge.kernel.org/AGL/release/halibut/)
See SPEC-3135 for more details.

It's more logical that the responsibility to the build process to create a JSON file each time a new SDK is publish under download.automotivelinux.org instead of having an external action that monitor and poll if a new SDK is available.

So my proposal is that this JSON file should be created in a specific directory (eg. https://download.automotivelinux.org/AGL/release/sdk and https://download.automotivelinux.org/AGL/snapshots/sdk/ ) each time a new SDK is available.
We can have either one JSON per SDK or a unique JSON file including all SDKs definition.

Here is an example of JSON file content :

{
    "name":         "AGL-release-guppy-7.0.4-qemuarm",
    "description":  "AGL SDK armv7vehf-neon-vfpv4 (version 7.0.4)",
    "profile":      "poky-agl",
    "version":      "7.0.4",
    "arch":         "armv7vehf-neon-vfpv4",
    "url":          "https://download.automotivelinux.org/AGL/release/guppy/7.0.4/qemuarm/deploy/sdk/poky-agl-glibc-x86_64-agl-demo-platform-crosssdk-armv7vehf-neon-vfpv4-toolchain-7.0.4.sh",
    "image_url":    "https://download.automotivelinux.org/AGL/release/guppy/7.0.4/qemuarm/deploy/images/qemuarm/agl-demo-platform-crosssdk-qemuarm-20190909144908.rootfs.tar.xz",
    "date":         "2018-10-11 18:21",
    "md5sum":       "46e6990d46162a870d12fc7a60c426e6"
}

Then XDS-server can easily retrieve this (or those) JSON file(s) and get the current list of available SDKs