Added add_foreign_utxo

To allow adding UTXOs external to the current wallet.
The caller must provide the psbt::Input so we can create a coherent PSBT
at the end and so this is compatible with existing PSBT workflows.

Main changes:

- There are now two types of UTXOs, local and foreign reflected in a
`Utxo` enum.
- `WeightedUtxo` now captures floating `(Utxo, usize)` tuples
- `CoinSelectionResult` now has methods on it for distinguishing between
local amount included vs total.

CHANGELOG.md

@@ -50,7 +50,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   type to mark for a missing client.
 - Upgrade `tokio` to `1.0`.
 
-#### Transaction Creation Overhaul
+### Transaction Creation Overhaul
 
 The `TxBuilder` is now created from the `build_tx` or `build_fee_bump` functions on wallet and the
 final transaction is created by calling `finish` on the builder.
@@ -61,6 +61,13 @@ final transaction is created by calling `finish` on the builder.
 - Added `Wallet::get_utxo`
 - Added `Wallet::get_descriptor_for_keychain`
 
+### `add_foreign_utxo`
+
+- Renamed `UTXO` to `LocalUtxo`
+- Added `WeightedUtxo` to replace floating `(UTXO, usize)`.
+- Added `Utxo` enum to incorporate both local utxos and foreign utxos
+- Added `TxBuilder::add_foreign_utxo` which allows adding a utxo external to the wallet.
+
 ### CLI
 #### Changed
 - Remove `cli.rs` module, `cli-utils` feature and `repl.rs` example; moved to new [`bdk-cli`](https://github.com/bitcoindevkit/bdk-cli) repository