Make ToLogParams an implementation detail

[mvukov]

The new logging functionality requires one to explicitly import rclrs::ToLogParams. I understand why is this needed, but, it looks to me like an impl detail. My Rust is not that good to judge whether this can be refactored or not... but the gist is: can we avoid that users have to import ToLogParams?

@geoff-imdex @mxgrey WDYT?

[mxgrey]

Importing ToLogParams can't be avoided because of limitations of the Rust language.

Generally I would recommend users to just put

use rclrs::*;

at the top of any modules where they will be using rclrs. If you do this then you won't need to explicitly import the trait.

We should consider also providing a prelude module so users can put use rclrs::prelude::*; to only import the most crucial structs and traits from rclrs.

[mxgrey]

But to be very precise, you only need to import ToLogParams if you want to build up custom log params. If you're okay with the default parameters then the following will all work without importing anything from rclrs:

rclrs::log!("my_app", "This is my log message");
rclrs::log!(node.logger(), "This is my log message");
rclrs::log!(&*node, "This is my log message");
rclrs::log_warn!("my_app", "This is my log message");
rclrs::log_error!("my_app", "This is my log message");

[mvukov]

The following should also work without the extra import of ToLogParams IIRC

rclrs::log_warn!(node.logger().name(), "This is my log message");

(which may be sufficient for some use-cases)

I am pro a prelude, that should reduce the boilerplate in the user code.