estimatesmartfee conf_target ("estimate_mode")

Estimates the approximate fee per kilobyte needed for a transaction to begin
confirmation within conf_target blocks if possible and return the number of blocks
for which the estimate is valid. Uses virtual transaction size as defined
in BIP 141 (witness data is discounted).

1. conf_target (numeric) Confirmation target in blocks (1 - 1008)
2. "estimate_mode" (string, optional, default=CONSERVATIVE) The fee estimate mode.
Whether to return a more conservative estimate which also satisfies
a longer history. A conservative estimate potentially returns a
higher feerate and is more likely to be sufficient for the desired
target, but is not as responsive to short term drops in the
prevailing fee market. Must be one of:
"UNSET" (defaults to CONSERVATIVE)

"feerate" : x.x, (numeric, optional) estimate fee rate in " + CURRENCY_UNIT + "/kB
"errors": [ str... ] (json array of strings, optional) Errors encountered during processing
"blocks" : n (numeric) block number where estimate was found

The request target will be clamped between 2 and the highest target
fee estimation is able to return based on how long it has been running.
An error is returned if not enough transactions and blocks
have been observed to make an estimate for any number of blocks.

> bitcoin-cli estimatesmartfee 6
Don't trust. Verify. Docs extracted from src/rpc/mining.cpp#L771-L804.