Update button to match current designs

What does this MR do?

The smallest MVC possible to solve !29775 (comment 327524279)

The goal would be:

• Maintain old button for the moment
• Allow the gitlab/ui empty_state.vue to be updated to use the new button. Currently it uses the deprecated_button
• Replace this old button with the new version once this is complete

This should give us 100% consistency during the migration of the rest of the empty state screens in the application.

Screenshots

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

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team