feat: add auto completion shell support for poststation-cli

[thaodt]

While playing around with Poststation, I thought it'd be nice if I could use <TAB> so the cli utils could suggest what args or sub-commands I should use next, this little PR supports that feature.

a small note here is that to maintain the current behavior of DeviceCommands, I've changed a little bit in Logs and LogsRange args from optional to default value, this is to avoid clap validation issue that required positional arguments must come before optional ones in the command definition.
otherwise it will cause an error when building similar to the following error:

thread 'main' panicked at /home/thaodinh/.cargo/registry/src/index.crates.io-6f17d22bba15001f/clap_builder-4.5.20/src/builder/debug_asserts.rs:638:17:
Found non-required positional argument with a lower index than a required positional argument: "count" index Some(1)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

please let me know if you think this is unreasonable.

Also the approach when generating specific shell auto-completion is to immediately process that command first instead of waiting for network connection and handle later. Because I think this feature does not need network connection to generate.

[thaodt]

hi @jamesmunns can you take a look on this?