add support for multiple log formats (#517)

this commit adds the tracing-subscriber crate and use its formatters to
support multiple log formats.

More details in
https://github.com/postgresml/pgcat/issues/464#issuecomment-1641430299

Signed-off-by: Sebastian Webber <sebastian@swebber.me>

src/lib.rs

@@ -1,13 +1,13 @@
 pub mod admin;
 pub mod auth_passthrough;
 pub mod client;
+pub mod cmd_args;
 pub mod config;
 pub mod constants;
 pub mod dns_cache;
 pub mod errors;
 pub mod messages;
 pub mod mirrors;
-pub mod multi_logger;
 pub mod plugins;
 pub mod pool;
 pub mod prometheus;