Mask job fields according to :read_build permission if in runner context

What does this MR do and why?

This MR ensures that only OKed job fields are visible for jobs requested from a project runner through the runner { jobs } GraphQL query. The reason is that a project runner can be assigned to many projects, and a user who can access the runner doesn't necessarily have permissions to look at the builds from all the projects that the runner executed. The Resolvers::Ci::RunnerJobsResolver is testing the :read_builds permission, but each individual job should also be authorized with :read_build.

I chose to mask the fields instead of removing the jobs themselves so that paging would work correctly, but also because it helps users to see how busy a runner is.

Changelog: fixed

Closes #410474 (closed)

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Before	After

Below is a comparison of the logs of the same GraphQL request (before & after):

We can see that the only change is an additional call to ProjectFeature Load for all the projects involved with the runners, due to the preload.

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