Migrate from BTC/kvB to sat/vB on RPC and startup options

This issue is motivated by the comments in https://github.com/bitcoin/bitcoin/issues/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 three 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`.
- Add a global init option to choose the units.

### List of Fee-Related Options and RPC Calls

#### Takes BTC/kvB as Argument
##### **Startup Options**
- [ ] `-consolidatefeerate`
- [ ] `-discardfee`
- [ ] `-fallbackfee`
- [ ] `-mintxfee`
- [x] `-paytxfee` (https://github.com/bitcoin/bitcoin/pull/31278)
- [ ] `-minrelaytxfee`
- [ ] `-blockmintxfee`

##### **RPC Calls**
- [ ] `sendrawtransaction`
- [ ] `submitpackage`
- [ ] `testmempoolaccept`
- [x] `settxfee` (https://github.com/bitcoin/bitcoin/pull/31278)

#### Prints BTC/kvB as a Result
##### **RPC Calls**
- [ ] `getmempoolinfo` ( https://github.com/bitcoin/bitcoin/pull/33741)
- [ ] `getnetworkinfo` (https://github.com/bitcoin/bitcoin/pull/33741)
- [ ] `analyzepsbt`
- [ ] `submitpackage`
- [ ] `testmempoolaccept`
- [ ] `estimatesmartfee` (https://github.com/bitcoin/bitcoin/pull/33741)
- [ ] `estimaterawfee` (https://github.com/bitcoin/bitcoin/pull/33741)
- [ ] `getwalletinfo` (https://github.com/bitcoin/bitcoin/pull/33741)

#### Prints BTC as Units for Fee Instead of Sats
##### **RPC Calls**
- [ ] `getmempoolinfo` (could make sense to keep BTC)
- [ ] `analyzepsbt`
- [ ] `createrawtransaction`
- [ ] `fundrawtransaction`
- [ ] `submitpackage`
- [ ] `testmempoolaccept`
- [ ] `walletcreatefundedpsbt`

Review the comments in issue #31088, then inventory the unchecked startup options and RPC calls listed here, using the linked pull requests for context. The work needs a chosen migration approach and an explicit affected-scope definition; done means the selected fee-unit behavior is applied consistently across the covered options and RPC results.

Written by the indexing model from the issue text.