Migrate SelfCert broadcast in DocumentsService

src/sakia/app.py

src/sakia/data/processors/identities.py

src/sakia/gui/dialogs/certification/controller.py

src/sakia/gui/dialogs/certification/model.py

src/sakia/gui/dialogs/connection_cfg/controller.py

src/sakia/gui/dialogs/connection_cfg/model.py

src/sakia/services/documents.py

src/sakia/tests/conftest.py

src/sakia/tests/functional/test_certification_dialog.py