add changelog

.changelog/2498.feature.md

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+Undisable transfers for some senders.
+
+Ostensibly for faucet purposes while we run the rest of the network with transfers disabled,
+this lets us identify a whitelist of accounts from which we allow transfers when otherwise transfers are disabled.
+
+Configure this with a map of allowed senders' public keys -> `true` in the new `undisable_transfers_from` field in the
+staking consensus parameters object along with `"disable_transfers": true`.