Add configurable max-savepoints and savepoint-interval

[emilcondrea]

Testnet4 has deep reorgs, causing ord to end-up in unrecoverable state. It would be good to have configurable reorg environment so it can be more aggressive on testnet4 but also not risk too much on mainnet. @raphjaph, this is related to #4169

[emilcondrea]

Looking a bit through existing reorgs on testnet4 some are of 15 blocks depth.

bitcoin-cli -chain=testnet4  getchaintips | jq -r '.[]|"\(.branchlen) \(.height)"'  | sort -n

...
8 65609
8 65609
8 65826
8 65927
8 66003
9 64845
9 65050
9 65334
9 65451
9 65451
9 65515
9 65515
9 65610
10 64846
10 65051
10 65051
10 65335
10 65452
10 65452
10 65452
10 65611
10 65611
10 65929
11 65336
11 65336
12 65613
12 65613
15 65616
15 65616

[raphjaph]

LGTM