Update CLI documentation for experimental environment variables

[bbabou]

The CLI documentation is missing some experimental environment variables that are defined in the codebase. Additionally, one legacy flag (OPENCODE_EXPERIMENTAL_BASH_MAX_OUTPUT_LENGTH) should be removed.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• doc: CLI environment-variables should add defualt value #5893: doc: CLI environment-variables should add default value

Feel free to ignore if none of these address your specific case.

[bbabou]

Working on a PR