include flash script inside backup img

Description

when creating and IMG zip, include everything we need to flash it ddepending on the device:

if no flash script, only include fastboot binaries

if a specific flash script is available, include it

Issue(s)

https://gitlab.e.foundation/e/devices/backlog/-/issues/189

Test procedures

Build with a pipeline on https://gitlab.e.foundation/e/priv/os/build/-/pipelines/new as branch alexandreroux-test

DEVICES: FP3 BRANCH_NAME: v1-q

resulting img zip should include binaries for linux and windows as well as a bash flash script

Check list

• Self review
• Test procedure explained
• Tested on fresh install