Support writing structured data directly, without JSON encoding

[reachfh]

Adds a new option to output the structured log message as a map instead of encoding it as JSON.

This works better when using a logger formatter that encodes all log messages as JSON, avoiding double encoding.
See my library logger_formatter_json.

With logger_formatter_json, the output is something like this:

{"msg":{"status":"200","path":"/","method":"GET","timing":"1ms","client_ip":"10.10.102.99","duration_ms":1.286,"x_forwarded_port":"443","x_forwarded_proto":"https","user_agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36","x_forwarded_for":"104.187.140.60"},"level":"info","file":"lib/uinta/plug.ex","line":"157","pid":"<0.3289.0>","request_id":"F6c-8tPDkCM2Ag4AAA4y","otel_trace_id":"659715447dcfbd23bc524d9bfc7a3992","otel_span_id":"e2e08b0504fbcc76"}

[epinault]

thank you for your contribution! I ll merge this after we fix the issue below and try to get a release later today. I will need to create a new minor and document the breaking change in the changelog

[epinault]

Fixed in #53. And just published a new version