`ghost_commit` config documentation update and backward compatibility

What is the type of issue?

_No response_

What is the issue?

There are two problems with the documentation on ghost_commit:

1. Contradictory default setting in code v.s. document: ghost-commit is on by default since recently https://github.com/openai/codex/commit/052b0528321232ad382c5c8be733fc70da70419c, while the docs below suggests otherwise:

https://developers.openai.com/codex/local-config/#supported-features
https://github.com/openai/codex/blob/main/docs/config.md#feature-flags

1. Its configuration key change to undo without documentation update: https://github.com/openai/codex/pull/6833

This also breaks backward compatibility as suggested here, especially given it is default on.

The backward compatibility concern was more for future. The documentation update might be an immediate benefit.

Where did you find it?

https://developers.openai.com/codex/local-config/#supported-features
https://github.com/openai/codex/blob/main/docs/config.md#feature-flags