[CI] test maintenance mode and shard retirement

[brenzi]

1. start single validateer
2. await ShardMode::Normal
3. shield 10 from //Charlie
4. register session-proxy for //Charlie (to increase consumers)
5. shield 10 from //Bob (should test more than one account)
6. sudo set maintenance mode for shard
7. await ShardMode::MaintenanceOngoing
8. transfer 1 from Charlie to Ferdie should fail (Filtered)
9. shield 11 from Charlie
10. verify balance: shielding should still work
11. await ShardMode::Retired
12. verfiy 21 went back to Charlie and 10 to Bob (minus fees)
13. shield 12 from Charlie
14. verfiy 12 went back to Charlie immediately (minus fees)extension: run on asset hub zombienet and test same with assets