Chore: Update kernel to 5.10

Firecracker supports Linux kernels 4.20 and 5.10.

This updates the Linux kernel used to 5.10.

The configuration is based on the Firecracker config [1]
on which `make menuconfig` is run to disable the following
fields: CONFIG_INPUT_KEYBOARD CONFIG_INPUT_MISC CONFIG_INPUT_FF_MEMLESS
and CONFIG_SERIO.

[1] https://github.com/firecracker-microvm/firecracker/blob/0fa080b137fd29e5bcd95073473b0a57c3868d86/resources/guest_configs/microvm-kernel-x86_64-5.10.config

.gitignore

@@ -21,3 +21,6 @@ node_modules
 /packaging/repositories/*/db/
 /packaging/repositories/*/dists/
 /packaging/repositories/*/pool/
+/kernels/linux-*/
+/kernels/linux-*.tar
+/kernels/linux-*.tar.sign

kernels/build-kernel.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+set -euf -o pipefail
+
+curl -OL "https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.10.124.tar.xz"
+curl -OL "https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.10.124.tar.sign"
+unxz linux-5.10.124.tar.xz
+
+gpg --locate-keys torvalds@kernel.org gregkh@kernel.org
+gpg --verify linux-5.10.124.tar.sign linux-5.10.124.tar
+
+tar -xvf linux-5.10.124.tar
+
+cp microvm-kernel-x86_64-5.10.config linux-5.10.124/.config
+
+cd linux-5.10.124/
+make menuconfig
+
+make -j32 vmlinux