cargo clippy catches common mistakes and improves the Rust code.
- Refactor: Add add_cargo_custom_target function to invoke a cargo command as custom target.
- Rename check-bitcoinsuite to check-bitcoinsuite-test to test bitcoinsuite crates.
- Add check-bitcoinsuite-clippy to lint bitcoinsuite crates.
- Add check-bitcoinsuite custom target that has the above two as dependencies.