CI: integrate tezos/opam-repository images, automatic approach

What

For full context, see the MR introducing the explicit approach: !12852.

In the automatic approach, we integrate the concept of "internal" and "external" images into the Tezos_ci module:

• Internal images are built in the same pipeline they are used (e.g. rust-toolchain).
• External images are built elsewhere (e.g. alpine:3.18) Internal images are associated with a image builder.

Whenever an internal image is used in the ~image: field of a job, the image builder is automatically included and a dependency added.

Furthermore, pipelines for protected branches must now be marked as such, and internal images are always rebuilt on such pipelines.

Why

How

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR