Resolve "Update $gray-200 value and usages"

What does this MR do?

1. Find/replace existing $gray-200 usages in gitlab to $gray-100 (this includes utility classes with gray-200)
2. Update value of $gray-200 from #dfdfdf to #bfbfbf

Conformity

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

Availability and Testing

N/A

Security

N/A

Closes #221301 (closed)