Add omdb expunge-testing fudge-serial <SLED_ID>

[jgallagher]

This subcommand should unblock looped sled add/expunge testing on madrid. After expunging, run this command to overwrite the serial numbers of the now-expunged sled, allowing it to be added again with its actual serial number.

This is obviously gross and should be removed once we solve #5625, which requires transitioning sleds to the decommissioned state.

There are some very primitive checks in place. Trying to fudge the serials for a sled that isn't expunged fails:

root@oxz_switch:~# ./omdb -w db expunge-testing fudge-serial 7bd6b802-e2d6-48bb-a53c-a7ee31f6e216
Error: serial number fudging only supported for expunged sleds; sled 7bd6b802-e2d6-48bb-a53c-a7ee31f6e216 has policy InService { provision_policy: Provisionable }

And trying to fudge the serials of the same sled twice fails:

root@oxz_switch:~# ./omdb -w db expunge-testing fudge-serial ac4a39a0-3dc5-4fc8-a7ad-5217af1b8f3d
Error: sled serial number (omdb-fudged-g2-0-1714162798) already appears fudged

[andrewjstone]

Just gross enough to work!

[jgallagher]

Closing this in favor of #5733 which should allow us to test this without this workaround