feat: add log statement indicating config source

[David Larsen (dc-larsen)]

Summary

• Adds an INFO-level log message that tells users where the configuration is being loaded from
• Tracks the config source internally via a _config_source key
• Outputs user-friendly descriptions for each source type

Config Sources

The three possible sources (in priority order) are:

1. Socket dashboard (API) - when using enterprise plan with dashboard config
2. JSON config file (--config) - when a config file is specified via CLI
3. Environment variables - the default when no other source is available

Example Output

2024-01-06 13:20:00 - INFO - Configuration loaded from: Socket dashboard (API)

or

2024-01-06 13:20:00 - INFO - Configuration loaded from: environment variables

Test plan

• Run socket-basics with no config (should show "environment variables")
• Run socket-basics with --config config.json (should show "JSON config file")
• Run socket-basics with API key and enterprise org (should show "Socket dashboard (API)")

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