Align container registry empty state with design guidelines

What does this MR do?

Fix the alignment of the empty Container Registry message and make sure it applies the design guidelines. Also, have split the commands into dedicated code blocks (with a copy button) to improve readability with longer commands.

Screenshots

New empty message (updated with monospace font):

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

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

Closes #64249 (closed)