Decide on gh-deploy

[pawamoy]

Two options:

• completely remove it (after deprecation period)
• move it as a third-party/sub-command (useful for initial work on subcommands, also see get-deps)

[pawamoy]

Related issues:

• Make the gh_deploy command and support multiple targets (i.e. PyPI) #431
• Add git commit -S i.e. signing support #891 (do we keep gh-deploy?)
• Allow file extensions to be configurable #930 (what for?)
• Avoid loading all docs in memory at the same time #2065 (would break many plugins)
• How to change to UTF 16 #2792
• Allow gh-deploy push w/o overwriting existing file in git #2796
• Add scoop or winget installation options #2891
• gh-deploy but don't push #3047
• Switch mkdocs and readthedocs themes into installable third-party-packages. #3190
• Add a more generic deploy command and deprecate gh-deploy #3373
• Docs enchancement: Update Deploying informations (add default configs for Github actions and Gitlab CI) #2144