feat: change default logging format to JSON

- Update default logging format from 'text' to 'json' in config.go
- Update config.example.yaml to use JSON format
- Update README.md example to show JSON format
- Align with other exporter projects that default to JSON logging

Author: d0ugal

README.md

@@ -22,7 +22,7 @@ server:
 
 logging:
   level: "info"
-  format: "text"
+  format: "json"
 
 metrics:
   collection:

config.example.yaml

@@ -4,7 +4,7 @@ server:
 
 logging:
   level: "info"
-  format: "text"
+  format: "json"
 
 metrics:
   collection:

internal/config/config.go

@@ -136,7 +136,7 @@ func LoadConfig(path string) (*Config, error) {
 	}
 
 	if config.Logging.Format == "" {
-		config.Logging.Format = "text"
+		config.Logging.Format = "json"
 	}
 
 	return &config, nil