feat(nextjs): Add post-build script for Vercel testing

[lobsterkatie]

This adds a script to be run after the nextjs app is built when testing an SDK branch on Vercel. More specifically, it

• moves the command to make the bundle analysis files available on the deployed app from a one-liner in the Vercel project settings to a script (because the code to do that correctly turns out to be a little more complicated than we thought),
• looks in the correct location for files created by experimental-serverless-trace builds, and
• only attempts to move the files if they exist.

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	22.33 KB (-0.01% 🔽)
@sentry/browser - Webpack	23.31 KB (0%)
@sentry/react - Webpack	23.34 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	29.79 KB (0%)

[kamilogorek]

Minor path change for consistency. You can also unify all echos to \nYour message\n if you want fewer lines, but I don't mind.

[lobsterkatie]

You can also unify all echos to \nYour message\n if you want fewer lines, but I don't mind.

Oh, man. Wouldn't I like to. I can't tell you how much time* I spent fighting with the shell on Vercel trying to get this to work. I can't remember the details - something about sh vs bash, though that wasn't the only issue - but nothing worked.

* My commit log from that time (related commits highlighted):

[kamilogorek]

Sorry, I expected too much from their environment 🥲