Make Docker-in-Docker the recommended and first-shown setup. Mounting the host's Docker socket gives every job root-equivalent access to the host, while DinD gives jobs their own daemon. The default `latest` tag is unchanged.
Also shorten the image flavour docs to what users need to pick an image, and correct that `dind-rootless` needs `--privileged` too.
Closes https://gitea.com/gitea/runner/issues/1227
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Co-authored-by: silverwind <[email protected]>
Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1258
Reviewed-by: silverwind <[email protected]>
Co-authored-by: bircni <[email protected]>