Move merge_conflicts to page specific styles

What does this MR do?

This MR moves the merge_conflicts.scss to a page specific bundle

Screenshots

🎉 It works
🎉 Even in dark mode
🐛 There's a preexisting issue where the button text isn't visible in "None" highlighting selected.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

References

• Related to #239852 (closed)