Move empty_rule into components directory

Issue: #201842 (closed)

What does this MR do?

This MR moves the empty_rule away from the mr-edit folder and into the general components folder. Why? Because this component is not specific to the MR edit, instead it is shared between MR edit AND Project Settings. So it is more appropriate to move it into the general components folder. Also, this will then be consistent with another similar component, empty_rule_name (which is also shared between MR edit and Project Settings)

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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

Closes #201842 (closed)