Support Logformat like json or logfmt

## Specific Demand if i have to parse the logs i have to write an regex. i would prefer json or [logfmt](https://brandur.org/logfmt) which are well formated and parse able logs ## Implement Suggestion use just the default [tracing_subscriber](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/) library for such formats: - **json** part of tracing-subscriber - [logfmt](https://docs.rs/tracing-logfmt/latest/tracing_logfmt/) more inforamation e.g.: https://oneuptime.com/blog/post/2026-01-25-structured-json-logs-tracing-rust/view to configure in dufs, maybe just set `--log-format=json` or `--log-format=logfmt`