update build tooling to make it build again
    
    There was an error:
    ```
    FATAL (antora): configuration param 'runtime.pull' not declared in the schema for /antora/site.yml (cwd: /antora, playbook: site.yml)
    ```
    Discussed here:
    https://discussion.fedoraproject.org/t/antora-v3-release-and-impact-on-fedora-docs/35788
    
    So update the config files and also drop `build.sh` and `preview.sh` and include
    `docsbuilder.sh` instead, from:
    https://pagure.io/fedora-docs/quick-docs