cln-plugin: Change default log level filter back to INFO

In commit 60e1532 (released in crate 0.1.8), which switched the
logging framework to tracing-subscriber, the default log level filter
was (accidentally) set to ERROR and above, instead of INFO and above.

Change this back to INFO as it was before. It can still be overridden
with CLN_PLUGIN_LOG.

Follows the example in https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#method.from_env

Closes ElementsProject#7658.

Changelog-Fixed: cln-plugin: Change default log level filter back to INFO

plugins/src/logging.rs

@@ -80,7 +80,10 @@ mod trace {
     where
         O: AsyncWrite + Send + Unpin + 'static,
     {
-        let filter = tracing_subscriber::filter::EnvFilter::from_env("CLN_PLUGIN_LOG");
+        let filter = tracing_subscriber::filter::EnvFilter::builder()
+            .with_default_directive(tracing_subscriber::filter::LevelFilter::INFO.into())
+            .with_env_var("CLN_PLUGIN_LOG")
+            .from_env_lossy();
         let sender = start_writer(out);
 
         tracing_subscriber::registry()