Make Secret Detection registry private

Why are we doing this work

As described in #470641 (closed), the container registry for development projects in the Secure group must be private.

Deprecation announcement - https://docs.gitlab.com/ee/update/deprecations.html#public-use-of-secure-container-registries-is-deprecated

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• Make the container registry private for the following projects
  • https://gitlab.com/gitlab-org/security-products/analyzers/secrets

Verification steps