Conan registry upload_urls endpoints

What does this MR do?

The Conan package manager client makes calls to a variety of endpoints when handling a package upload. This MR implements the upload_urls endpoints as described in #13345 (closed). Each endpoint returns a set of urls that the Conan client will eventually use to upload the files listed in each endpoint. This MR also creates the basic skeleton API endpoints for what's known as the "snapshot" and "manifest" (digest) endpoints. As a first step, the /digest endpoints will return a 404 as this is what the Conan client expects when no package currently exists in the remote registry (GitLab). The recipe snapshot endpoints return an empty hash or object {} for the same reasons. These endpoints will be expanded in a separate MR.

Note: This MR is set to be merged into !16215 (merged) as it contains code that this MR builds upon. Should that MR get merged first, I will be updating so this MR is merged into master.

Screenshots

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

Related #13345 (closed), !16215 (merged)