Add `sign` sub-command in aggregator `genesis` command #1769

All 640 tests pass in 7m 0s

    3 files ±0   16 suites ±0 7m 0s ⏱️ + 1m 4s
640 tests +1 640 ✔️ +1 0 💤 ±0 0 ❌ ±0
678 runs +1 678 ✔️ +1 0 💤 ±0 0 ❌ ±0

Results for commit b3c67e4. ± Comparison against earlier commit f626768.