This issue is motivated by the comments in #31088

Most of the RPC and Startup options use BTC/kvB while the "standardized" units by users and other softwares is sats/vB.
Note that updating to sat/vB can be backward incompatible in some cases.

There are two approaches that can be followed:

• Update all to sat/vB even if that is not backward compatible (all in the same release). This has been done before with bumpfee and psbtbumpfee, before v0.21 were using BTC/kvB and after moved to sats/vB.
• Add an option to use sats/vB but don't remove BTC/kvB. This has been done before with fundrawtransaction and walletcreatefundedpsbt.

List of Fee-Related Options and RPC Calls

Takes BTC/kvB as Argument

Startup Options

• -consolidatefeerate
• -discardfee
• -fallbackfee
• -mintxfee
• -paytxfee (wallet, rpc: deprecate settxfee and paytxfee #31278)
• -minrelaytxfee
• -blockmintxfee

RPC Calls

• sendrawtransaction
• submitpackage
• testmempoolaccept
• settxfee (wallet, rpc: deprecate settxfee and paytxfee #31278)

Prints BTC/kvB as a Result

RPC Calls

• getmempoolinfo
• getnetworkinfo
• analyzepsbt
• submitpackage
• testmempoolaccept
• estimatesmartfee
• getwalletinfo

Prints BTC as Units for Fee Instead of Sats

RPC Calls

• getmempoolinfo (could make sense to keep BTC)
• analyzepsbt
• createrawtransaction
• fundrawtransaction
• submitpackage
• testmempoolaccept
• walletcreatefundedpsbt