Release Guide Pages for 3.0

[thunderbiscuit]

Keeping track of the features we want to highlight in the 3.0 Release Guide.

• Persisting locking of UTXOs feat!: Persist utxo lock status bdk_wallet#259
• Wallet::update returns Events Return wallet events when applying updates and blocks (3.0 milestone) bdk_wallet#319
• Addition of Wallet::create_psbt Implement create_psbt for Wallet bdk_wallet#297
• Support for export to Caravan wallets
• The signers are deprecated in 3.0. Page on how to do it with Psbt::sign
• Removal of Wallet::cancel_tx refactor(wallet)!: Remove Wallet::cancel_tx function bdk_wallet#393
• Compatibility guarantees docs(changeset): Add section on version compatibility bdk_wallet#391