feat(sidekick): new sidekick config

[rofe]

Prep for adobe/helix-sidekick#14

Test drive using the following bookmarklet URL:

javascript:/* ** Helix Sidekick Bookmarklet ** */(() %3D> %7Bconst c%3D%7B"owner":"adobe","repo":"theblog","ref":"sk-cfg"%7D%3Bconst s%3Ddocument.createElement(%27script%27)%3Bs.id%3D%27hlx-sk-app%27%3Bs.src%3D%27https://sidekick-updates--helix-pages--adobe.hlx.page/tools/sidekick/app.js%27%3Bs.dataset.config%3DJSON.stringify(c)%3Bif(document.getElementById(%27hlx-sk-app%27))%7Bdocument.getElementById(%27hlx-sk-app%27).replaceWith(s)%3B%7D else %7Bdocument.head.append(s)%3B%7D%7D)()%3B