Feat: Added custom headers and toggle keyring CLI options

[BlairAllan]

Summary

Add support for custom HTTP headers and a CLI option to toggle keyring storage. Updated docs to explain how to add these headers and provided an example.

Type of Change

• [x] Feature

Testing

• Added unit tests for custom headers in custom_providers.rs to verify that the headers are saved and loaded correctly
• Manually tested the CLI flow for adding custom headers
• Manually tested the keyring toggle functionality via goose configure > Settings > Secret Storage

[taniandjerry]

Let us know when this is ready for review, or if you have questions!

[blackgirlbytes]

here's how to fix the DCO check

[DOsinga]

sorry @BlairAllan for letting this linger - there was a merge conflict I tried to fix, but we changed the interface and I think I made it worse. can you have a look?

[DOsinga]

there's a linter error now @BlairAllan

[BlairAllan]

there's a linter error now @BlairAllan

This should all be fixed now