SCSS - update badge color for new plans

What does this MR do?

As part of #321364 (closed), we introducing Premium and Ultimate plans into the database (MR here). Today, we already are showing new plans (eg. Premium (formerly Silver)), but behind the scenes, this group still points to an old plan (eg. Silver) in the database.

Before we start pointing to the new plans records, we need to update color codes used to render Silver and Gold badges, while at the same time keep the codes for the old plans. This is what this MR does.

Screenshots (strongly suggested)

A couple of screenshots to show that color codes still work for both old (deprecated) and new plans.

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

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #321364 (closed)