[log][v2] expose formatter option

[BTMuli]

As the img above show,it is useless for developer or user to see the line of the log,the real matter thing should occupy more space.

[Legend-Master]

We do have that: https://docs.rs/tauri-plugin-log/latest/tauri_plugin_log/struct.Builder.html#method.format

[BTMuli]

We have that: https://docs.rs/tauri-plugin-log/latest/tauri_plugin_log/struct.Builder.html#method.format

It is rust ver and has no example.😢

[Legend-Master]

Well, it's really not very efficient to sending the log to the webview and then getting it back since there can be a lot of them, so that's why it's only in the rust side, for the examples, we currently use fern under the hood, so you can take a look at https://docs.rs/fern/latest/fern/struct.Dispatch.html#method.format for now, we'll need more documentations on this though