util/liveiso: Add NixOS configs for bootable live systems

Add NixOS configurations for bootable live systems containing a set of
tools which might be useful for firmware development in general and for
working on coreboot.

There are two configurations provided. One for console-only and a
graphical one, which is mostly the same as the console image but it
comes with Gnome Shell as window manager and some graphical tools in
addition.

An image can be built using `build-console.sh`, respectively
`build-graphical.sh`. The resulting iso image can be found in
`result/iso/`.

The console image results in ~700MB, while the graphical one results in
~2GB.

Change-Id: Iaf49d198e99781434bd89d2a8a125a4988b77e1c
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50194
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index a902adc..b202a52 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -775,6 +775,11 @@
 S:	Maintained
 F:	util/me_cleaner/
 
+LIVEISO
+M:	Felix Singer <felixsinger@posteo.net>
+S:	Supported
+F:	util/liveiso/
+
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 # Miscellaneous
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