Documenting backup workflows and actions in backups.md

[mansueli]

What kind of change does this PR introduce?

What is the current behavior?

Please link any relevant issues here.

What is the new behavior?

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[wyozi]

@kiwicopple @mansueli this is imo simply a bad idea and kind of weird to have in official Supabase docs, as if you were advocating this.

Few reasons:

• Git repos are just not the right place to store backups. In addition, Github has a 100mb limit so this will fail for any reasonable sized database
• Storing customer data in form of backups in a Git repo also is weird. Almost like storing access tokens in .env files committed to Git remote
• The example action is just implemented weird. Why would you want backup action to be triggered by this: "the action will run whenever a new PR is created."? Why is it triggered by pushes to the repo as well?

I would suggest either changing this to something more reasonable (like uploading backups to s3 in a github action, which is a bit weird but less weird) or just removing it altogether.