[IN PROGRESS] Replace Vercel bot with proper GitHub actions

[ohadschn]

We now have 2 pipeline systems that do the same thing (next build), conceptually it's bad, for example off the top of my head:

1. Vercel bot config is completely implicit / hidden / unclear. Beyond the obvious issue, it might also cimplicate things like Environment configuration (local VS preview VS prod) #290.
2. It's just a matter of time until they go out of sync, for example PR sync passes but Vercel deployment fails.
3. It creates issues with Vercel accounts, e.g. PR builds not being deployed if issuer isn't on the Vercel team (and even if they are on the team and the build fails, they can't access the logs)

Yes, the bot was convenient for the initial setup, but for proper development workflow I think it does more harm than good.

Examples

1. I can't be 100% sure, but we might already have an example of bullet (2) above (Vercel build fails, PR build succeeded): https://vercel.com/4tals/iron-links/55W25BcSGwDj73Tqk744JeAG8yJk?utm_medium=email&utm_source=notifications
2. For some reason the Vercel bot refuses to deploy the following PR (I approved it 20 times already): Auto pr improvements #399

[ohadschn]

I can't be 100% sure, but we might already have an example of bullet (2) above (Vercel build fails, PR build succeeded):
https://vercel.com/4tals/iron-links/55W25BcSGwDj73Tqk744JeAG8yJk?utm_medium=email&utm_source=notifications

[ohadschn]

@4tal can you please post here the logs for some sample Vercel CI/CD run from the Vercel portal? Specifically:

• vercel build command & output
• vercel deployy command + output