build: profiles.json: add kernel version information

build: profiles.json: add kernel version information

Currently downstream tools like ASU lack information about kernel
version to find out the relevant kmod build folder on downloads server.

So lets fix it by providing a new `linux_kernel` JSON array which would
for the start provide Linux kernel version, revision and vermagic
information.

  "linux_kernel": {
     "release": "1",
     "vermagic": "b57450c07d3a786158c3601fc5cee57d",
     "version": "6.6.61"
   },

Fixes: openwrt/openwrt#17036
Fixes: efahl/owut#9
Co-developed-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Eric Fahlgren <ericfahlgren@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17042
Signed-off-by: Petr Štetiar <ynezz@true.cz>