bug#27007: boot-parameters are not documented

[Mathieu Othacehe]

Hi Ludo,

Since the rework, <menu-entry> are in (gnu bootloader grub). They can no
longer be used in menu-entries field of <bootloader-configuration>.

The <boot-parameters> is used instead. <boot-parameters> and
<menu-entry> are very similar though.

What we can do here is :

* Give <boot-parameters> default values as per <menu-entry> (as proposed
by Danny in doc patch review).
* Rename "menu-entries" field of <bootloader-configuration> to something
not so GRUB related, such as "entries" or "custom-entries".
* Maybe also remove <menu-entry> from (gnu bootloader grub) and use
<boot-parameters> directly as in (gnu bootloader extlinux).

WDYT ?

Thanks,

Mathieu