systemd-boot: Make automatic entries configurable

systemd-boot: Make automatic entries configurable

Hiding automatic entries allows for giving custom entry names like
"Windows 10" instead of "Windows Boot Manager" by creating an appropriate
loader file in the loader/entries folder.
Note that it is already doable by renaming bootmgfw.efi (or the other auto-detected
boot loaders) and then using the renamed file for a custom entry. But windows will
automatically recreate the boot loader on updates, including the default EFI
bootloader entry if that one is missing.

Make hiding EFI reboot a separate option because there is no simple way to create
it with a custom loader entry and people may still want that around while still
hiding the other auto entries.

Also, turn no_editor into a positive boolean name while we're touching this code.