(RHEL-66582) feat(dracut.sh): add --add-confdir option

[pvalena]

When generating kdump's initrd, we want to keep [omit_]dracutmodules
empty and let kdump to handle the modules. And we don't want to
affect the first kernel's initrd, so we cannot place our conf file
to /etc/dracut.conf.d or /usr/lib/dracut/dracut.conf.d.

This patch adds a new option to allow user to add an extra configuration
directory to use *.conf files from. If the dir not exists, will look for
confdir's subdir.

After that, kdump can use "--add-confdir kdump" if
/usr/lib/dracut/dracut.conf.d/kdump exists, to apply its own dracut conf.

See also:
rhkdump/kdump-utils#11
rhkdump/kdump-utils#31

Suggested-by: Dave Young [email protected]
Signed-off-by: Lichen Liu [email protected]

(cherry picked from commit ae81535037c42b716d8cbb9dc18942b5c6f16fed)

Resolves: RHEL-66582

[github-actions]

Commit validation

Tracker - RHEL-66582

The following commits meet all requirements

commit	upstream
3412ef4 - fix: typo in variable name	dracutdevs/dracut@76b2f1a

The following commits need an inspection

commit	note
48b323e - feat(dracut.sh): add --add-confdir option	Missing upstream reference ‼️

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Tracker validation

Success

🟢 Tracker RHEL-66582 has set desired product: rhel-9.6
🟢 Tracker RHEL-66582 has set desired component: dracut
🟢 Tracker RHEL-66582 has been approved
🟢 Tracker RHEL-66582 has set severity

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[pvalena]

LGTM.