Which issue does this PR close?

Closes #4918.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

Breaking changes: This PR removes with_error_level(), with_failure_level() and with_backtrace_output() from the DefaultLoggingLayer.

It adds a new trait LoggingInterceptor to log messages.

pub trait LoggingInterceptor: Debug + Send + Sync + 'static {
    fn log(
        &self,
        scheme: Scheme,
        operation: Operation,
        path: &str,
        context: &str,
        message: &str,
        err: Option<&Error>,
    );
}

The LoggingLayer has a new method to construct a new layer from an interceptor.

fn new<I: LoggingInterceptor>(notify: I) -> LoggingLayer<I> {}