feat(MDX): add optional hard breaks option

[eaglethrost]

🎫 Resolve CX-2095

Summary

• Adds an optional hardBreaks flag to the MDX compile() function that enables remark-breaks, converting soft line breaks (\n) into hard breaks (<br>)
• This would allow text like hello \n there to be split now
• Disabled by default to preserve existing behavior, different app components can opt in as needed

Context

The legacy rendering engine parsed newline characters as line breaks. Some customers want this behaviour in refactored, such as in API descriptions in the API explorer (see attached linear ticket), hence we should have an option in the MDX rendering to allow that. See also this linear comment: https://linear.app/readme-io/issue/CX-2095/line-break-characters-in-descriptions-arent-being-processed-correctly#comment-a6580c9e

If we agree to do this, we would need to also update the readme side to use the new flag for UI areas that need this behaviour.