cmd/geth: add ability to get/put raw db values

[holiman]

This PR is a bit experimental, and provides ability to modify the database contents. It's for being able to inspect, and potentially salvage, problems like reported in #21990 .
Example usage:

Putting a value

[user@work go-ethereum]$ ./build/bin/geth db.put 0x1337 0xdeadc0de
INFO [12-10|11:02:19.555] Maximum peer count                       ETH=50 LES=0 total=50
INFO [12-10|11:02:19.555] Smartcard socket not found, disabling    err="stat /run/pcscd/pcscd.comm: no such file or directory"
...
..
INFO [12-10|11:02:19.598] Opened ancient database                  database=/home/user/.ethereum/geth/chaindata/ancient
INFO [12-10|11:02:19.599] Freezer shutting down

Reading it:

[user@work go-ethereum]$ ./build/bin/geth db.get 0x1337
INFO [12-10|11:02:27.926] Maximum peer count                       ETH=50 LES=0 total=50
...
INFO [12-10|11:02:27.953] Opened ancient database                  database=/home/user/.ethereum/geth/chaindata/ancient
key 1337:
        deadc0de
INFO [12-10|11:02:27.955] Freezer shutting down

Overwriting it:

[user@work go-ethereum]$ ./build/bin/geth db.put 0x1337 0xcafebabe
INFO [12-10|11:02:36.959] Maximum peer count                       ETH=50 LES=0 total=50
...
INFO [12-10|11:02:36.987] Opened ancient database                  database=/home/user/.ethereum/geth/chaindata/ancient
Previous value:
deadc0de
INFO [12-10|11:02:36.988] Freezer shutting down

[holiman]

Closed in favour of #22014