Added initial Diffblue Cover integration

app/controllers/concerns/integrations/params.rb

app/models/ci/build.rb

app/models/integration.rb

app/models/integrations/diffblue_cover.rb

app/models/project.rb

...ounts_all/20231205140200_groups_diffblue_cover_active.yml

...0231205140200_groups_inheriting_diffblue_cover_active.yml

...ts_all/20231205140200_instances_diffblue_cover_active.yml

...nts_all/20231205140200_projects_diffblue_cover_active.yml

...31205140200_projects_inheriting_diffblue_cover_active.yml

db/docs/integrations.yml

doc/.vale/gitlab/spelling-exceptions.txt

doc/api/graphql/reference/index.md

doc/integration/diffblue-cover.md

doc/integration/img/diffblue_cover_diff_v16_8.png

doc/integration/img/diffblue_cover_workflow_after_v16_8.png

lib/api/helpers/integrations_helpers.rb

locale/gitlab.pot

spec/factories/integrations.rb

spec/lib/gitlab/import_export/all_models.yml