[generator] [kadeploy] Allow to configure the install_bootloader script

Caution: we set no default value, so the g5k configuration (in g5k-platform-production) needs to be updated!

Depends on https://gitlab.inria.fr/grid5000/g5k-platform-production/-/merge_requests/54

added 7 commits

• ba8c3fd4...800061a1 - 6 commits from branch master
• 594c8e70 - [generator] [kadeploy] Allow to configure the install_bootloader script

Compare with previous version

merged

mentioned in commit dd5d6009