Remove action.parabol.co hardcoded in app

[mattkrick]

Our app is deployed to many hosts.
It's here, but also other places: https://github.com/ParabolInc/parabol/blob/b656e7d44061aabd78abadfb05e79d61de9bd181/packages/client/modules/email/components/SummaryEmail/MeetingSummaryEmail/LogoFooter.tsx

AC

• use process.env.HOST instead

[mattkrick]

#8557 (review)

[BartoszJarocki]

@mattkrick should we remove this from our squad board then?

[mattkrick]

sure, i'll take this one. still not sure what to do with those static assets that aren't directly tied to a build, but we'll figure something out!

[mattkrick]

Plan of attack:

• put EVERYTHING in the build
• push all assets to the same bucket, do not use a versioned subdirectory (already done in chore: Build once, run everywhere #8557)
• optional: check if exists before pushing to speed up pushes
• when webpack touches images, keep their file name or maybe filename + a content hash.