1141: feat: compile bootloader examples for nRF91 r=lulf a=lulf
* Add nRF91 as target in CI builds
* Add example linker scripts for nrf91
* Make less nRF52 assumptions example config
* Add llvm-tools-preview required for cargo objcopy example
Co-authored-by: Ulf Lilleengen <lulf@redhat.com>