update pulumi branding on github app docs page

[susanev]

File: themes/default/content/docs/guides/continuous-delivery/github-app.md

a few of the screenshots need updating with the new logo, we should also remove the see below link.

also, check with @gthuang if this is the correct marketing content..

[susanev]

🤔 i do not remember writing this, but there was another issue that fixed this recently as part of the deploy launch, so closing.

[susanev]

oh lol this is in hugo