Feature/custom log formatting

[mrtzgh]

Add Configurable Log Formatting Options for Supervisor

Fixes #553 - This PR implements highly requested log formatting configuration options for Supervisor, addressing community feedback.

What's New

Two new configuration options:

• logfile_format - Customizes main supervisord log messages
• childlog_format - Customizes child process log messages (stdout/stderr)

Both support Python logging format strings with placeholders like %(asctime)s, %(levelname)s, %(process)d, etc.

Example Usage

[supervisord]
logfile_format=%(asctime)s [%(levelname)s] [PID:%(process)d] %(message)s
childlog_format=%(asctime)s [CHILD] %(message)s

Output:

# Main log
2024-01-15 10:30:15,123 [INFO] [PID:1234] supervisord started with pid 1234

# Child logs
2024-01-15 10:30:16,456 [CHILD] Starting application server

Key Features

backward compatible - existing configs work unchanged
error handling - invalid formats fall back to defaults
tests - all existing tests pass + new coverage
documentation - examples, best practices, troubleshooting

Benefits

• Enhanced debugging with timestamps and PIDs
• Better integration with log aggregation systems (ELK, Splunk, etc.)
• Support for compliance logging requirements
• Customizable formats for specific operational needs

This addresses a long-standing community request for better control over Supervisor's logging output while maintaining full compatibility.