sys-boot/grub: update to 2.06

[sayanchowdhury]

sys-boot/grub: update to 2.06

Fixes flatcar/Flatcar#1099

Testing done

CI Passed (except for few arches) http://jenkins.infra.kinvolk.io:8080/job/container/job/sdk/1009/cldsv/
CI Running
http://jenkins.infra.kinvolk.io:8080/job/container/job/sdk/1013/cldsv/

Reviews from the previous PR flatcar-archive/coreos-overlay#2098

• @krnowak
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - Fixed
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - Fixed
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - This seems to be required, and this is required to construct IUSE, and MULTIBUILD variant used in the ebuild
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - Fixed this

• @pothos
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - I've fixed the commits, and have added a README.md file adding a bit of context as well as the list of commits picked.
  sys-boot/grub: sync with gentoo upstream; updates to 2.06 flatcar-archive/coreos-overlay#2098 (comment) - Tested and looks good, the downgrade worked successfully but did not affect the grub, which stayed at 2.06

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)

• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[sayanchowdhury]

Another fresh CI builds with the accomodated patches: http://jenkins.infra.kinvolk.io:8080/job/container/job/sdk/1013/

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/5961101552

[jepio]

lgtm - lets review the getenv thing when we update shim and get secure boot working.