Resolve "Conan Skeleton API"

What does this MR do?

This change creates a new API endpoint for Conan packages. It is a simple Ping endpoint to build a first iteration towards the overall Conan API and feature. The endpoint sits behind a feature flag, and requires packages be enabled (from license). The expected behavior is 404 Not Found if the feature flag is not enabled, and 401 Unauthorized if the flag is enabled. Authorization will be handled in the next issue/MR: https://gitlab.com/gitlab-org/gitlab-ee/issues/12568

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

Directly Related: #12567 (closed) Related: https://gitlab.com/gitlab-org/gitlab-ee/issues/8248