Add postgres upgrade script from 9.6 to 14

[hubertdeng123]

This PR adds an upgrade script for postgres from 9.6 to 14.

https://github.com/getsentry/self-hosted/issues/1610

[BYK]

Related: #1705. I think instead of introducing a postgres version variable, it would be better to introduce a hard-stop upgrade point, add the script there, and then remove it afterwards.

[hubertdeng123]

Going to put this on the backlog for now to work on dogfooding, ran this script and it seems to work just fine. Introducing a hard-stop upgrade will take more time to investigate

[aminvakil]

Related: #1705. I think instead of introducing a postgres version variable, it would be better to introduce a hard-stop upgrade point, add the script there, and then remove it afterwards.

What's wrong with users being able to upgrade from any self-hosted version using 9.6 to any self-hosted version post merging this which uses 14? So we won't need a hard-stop right?

[github-actions[bot]]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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