Add stress test to weekly build

[Shpinkso]

Acceptance

• Runs on weekly builds only (not CI)
• Runs the following for 12 hours
  stress --cpu 20 --io 20 --vm 4 --vm-bytes 16M & iperf3 -c <test-server-ip> -b0 -t0 -i 10 &
• Flags a failure if the board crashes /coredumps/becomes unresponsive

[Ham22]

I'd be tempted to set this up as a separate soak test system that just runs permanently? Weekly builds could just bump the SW being tested but would be nice to have a continuous stream of dumps/debug being reported.

[Shpinkso]

we can set that up fairly easily once we have this working - but don't want the physical setup to be a blocker for the first test