feature request: #[backtrace] attr add force option

[Sherlock-Holo]

currently the #[backtrace] attr has no option, and thiserror generated codes always use Backtrace::capture()

however, if user want some error always enable backtrace, they have to

• write impl From<Err> Error manually
• or set env RUST_BACKTRACE=1, but that will cause all backtraces are enabled, even they only want to enable a few error backtrace

if #[backtrace] add a new option force, like #[backtrace(force=true)], when user enable the force capture, thiserror generated codes can use Backtrace::force_capture() instead of Backtrace::capture()