automatically redirect to GH_PAT and other secret setup where appropriate

[maxheld83]

applies to most deploy functions

[maxheld83]

or at least a warning like so:

usethis::ui_todo(c(
    "Remember to provide `GH_PAT` as a secret to the GitHub UI.",
    "For more information about Personal Access Token (PAT) for ghpages go to {usethis::ui_path('https://github.com/maxheld83/ghpages')}.",
    "See {usethis::ui_code('usethis::browse_github_pat()')} for help setting this up."
  ))