Calculated default level when user gave custom levels and doesnt specify level property in logger.

[Muhammad-Abdullah-shahzad]

Summary

• Adds automatic default level calculation when createLogger() is called with custom levels but no level specified.
• Ensures that the logger defaults to the median level if no level is provided.
• Adds Jest unit tests to verify the default level behavior with different custom levels and the silent option.

Tests

• 4 unit tests covering:
  1.should default to low level if level not specified.
  2. Default to fourth level in multi-level custom config.
  3.Should default to second level if level specified.
  4. should default to info level if level not specified and levels not specified

Motivation

This improves usability for developers using custom log levels without needing to explicitly set a default value.
if developer explicitly gives a level value it will override default level value.

[Muhammad-Abdullah-shahzad]

@indexzero I've created a pr addressing the issue #1491.Please have a look and let me know if changes required.