Expose `has_trace` in job API

Problem to solve

Expose has_trace inside of Project::JobController#show.json as part of #50101 (closed)

Further details

app/views/projects/jobs/show.html.haml has the following conditions which frontend needs to migrate to vue, adding has_trace in the response as a boolean field that is always present, they should be able to used that to have the same logic.

    - if @build.running? || @build.has_trace?
      .build-trace-container.prepend-top-default
        .top-bar.js-top-bar
          .js-truncated-info.truncated-info.d-none.d-sm-block.float-left.hidden<
            Showing last
            %span.js-truncated-info-size.truncated-info-size><
            of log -
            %a.js-raw-link.raw-link{ href: raw_project_job_path(@project, @build) }>< Complete Raw

          .controllers.float-right
            - if @build.has_trace?
              = link_to raw_project_job_path(@project, @build),
                      title: 'Show complete raw',
                      data: { placement: 'top', container: 'body' },
                      class: 'js-raw-link-controller has-tooltip controllers-buttons' do
                = icon('file-text-o')