CI: split build and deploy documentation, use artifacts

        WITH_PYTHON: "yes"

build documentation:

    stage: build

    only:

        changes:

            - Documentation/**/*

            - src/TNL/**/*.{h,hpp}

    script:

        - ./Documentation/build

    artifacts:

        paths:

            - ./Documentation/html/

    tags:

        - doxygen

deploy documentation:

    stage: deploy

    only:

        variables:

            - $TNL_DOC_DEPLOY_KEY

        changes:

            - Documentation/**/*

            - src/TNL/**/*.{h,hpp}

        refs:

            - develop

            - schedules

            - triggers

    dependencies:

        - build documentation

    script:

        - ./Documentation/build

        - ./Documentation/deploy

    tags:

        - doxygen