Account for bls grub changes in upstream

[phillxnet]

There are movement a-foot re bls capabilities/options within grub/kiwi-ng. These have recently culminated in kiwi-ng 10.0.14's requirement to specify a preference re bls within our kiwi-ng config: given we are openSUSE based and upstream kiwi-ng's 'sensitivities' here pertain to rpm distributions of kiwi-ng only. Where-as to obtain, and containerise, the latest version of Kiwi-NG we install via PIPX / PyPi within our installer builder back-end and our README.md instructions guide folks to use a venv (PyPi).

See v10.0.14's doc entry re bls=”true|false”: https://osinside.github.io/kiwi/image_description/elements.html#image

bls=”true|false”:

Specifies whether to use Bootloader Spec-style configuration if grub in the image supports it. It is a no-op if the blscfg module is not available. This option is only available for grub and defaults to true if not set.

[phillxnet]

From the sensitivities link above, we need:

bls=”false”

to account for our, and potentially others, non rpm installed kiwi-ng; and our "Built on openSUSE" nature.