Add links to initrd and rootfs

[probonopd]

On the boot details page (e.g., https://kernelci.org/boot/id/5bd738a859b514802674be00/), please add add links to initrd and rootfs in addition to zImage and dtb, so that one can reproduce the exact boot using real hardware at home.

[probonopd]

According to IRC, the kernel build directory for this build is: https://storage.kernelci.org/mainline/master/v4.19-9418-g9f51ae62c84a/arm/multi_v7_defconfig/. The initrd is created by LAVA and is temporary (not available for download). But it's simple: extract the initrd (https://storage.kernelci.org/images/rootfs/buildroot/armel/), extract the modules on top of it, and repack the initrd.