ci(docs): use push-to-fork when creating pr

[crazy-max]

follow-up docker/buildx#1184

increase security so docker-tools-robot does not need write access on docker/docker.github.io and will push to its own fork at https://github.com/docker-tools-robot/docker.github.io and create the PR from it.

unfortunately we can't set the label anymore as it requires admin rights but I think it's fine:

  Applying labels 'area/Build'
  Error: Must have admin rights to Repository.

other advantage is it will not pollute docker/docker.github.io with other branches.

cc @glours

Signed-off-by: CrazyMax crazy-max@users.noreply.github.com

[crazy-max]

ci issue unrelated: https://github.com/docker/compose/runs/7469589600?check_suite_focus=true#step:5:89

run golangci-lint
  Running [/home/runner/golangci-lint-1.47.2-linux-amd64/golangci-lint run --out-format=github-actions --timeout=180s] in [] ...
  Error: `addSecretsConfig` - `sessionConfig` is unused (unparam)
  
  level=warning msg="[linters context] structcheck is disabled because of go1.18. You can track the evolution of the go1.18 support by following the https://github.com/golangci/golangci-lint/issues/2649."
  
  Error: issues found

[glours]

LGTM