Add static grub config

[cgwalters]

This pairs with coreos/bootupd#543 to have bootupd support injecting the greenboot grub logic only if greenboot is installed.

[nullr0ute]

How does this impact users that may not have moved to bootupd/unified core yet?

[LorbusChris]

To add some more context: This config snippet originates with grub2-tools, but it's excluded in FCOS.
I'm not familiar with the reasons of osbuild carrying another copy of that snippet.

Desktop variants currently use:

• 10_reset_boot_success
• 12_menu_auto_hide
• 14_menu_show_once
  (It looks like there's an effort to drop 12_menu_auto_hide eventually in favor of 14_menu_show_once)

How would these snippets be shipped for e.g. the Silverblue ostree native container image? Do all the snippets have to shipped in /usr/lib/bootupd/grub2-static/configs.d/ going forward in order to work with bootupd? How are they ordered?

Should 08_fallback_counting be removed from grub2-tools after this merges to make this repo here the canonical location?

[cgwalters]

How does this impact users that may not have moved to bootupd/unified core yet?

If bootupd isn't used (as it's not today for IoT/Edge) there is zero impact other than a small new file in /usr that is unused.

To add some more context: This config snippet originates with grub2-tools, but it's excluded in FCOS. I'm not familiar with the reasons of osbuild carrying another copy of that snippet.

So one thing going on here is many of us really want a "static grub config" where we don't run grub2-mkconfig and especially not os-prober for every kernel update.

[cgwalters]

cc ostreedev/ostree#3162 (comment)

[runcom]

Given low impact as per #129 (comment) and since we're moving to bootupd, this ease with testing that flow too.

lgtm