Resolve "Special characters in project name/path prevent users from using the container registry"

What does this MR do?

This updates the Vue component on the registry page so that it can show specific messages for the following scenarios:

• When there are no containers in the registry
• When there is an issue connecting to docker due to unsupported characters in the project name/path

The documentation content that was on this registry page has also been removed as per issue: #62770 (closed)

The backend changes that were made to support the new error message will need confirming by a backend engineer and possibly refactored.

A new test was added to app_spec.js to test the display of the new invalid characters error message.

Screenshots

Empty registry

Invalid characters error

User documentation

Admin documentation

Does this MR meet the acceptance criteria?

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 #45104 (closed) Closes #62770 (closed)