Add Cache_Control private header to server responses

[MonkeyDo]

We have seen issues where it seems that a user's cookies are sent to the wrong user, making it appear like you are logged into another user's account. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching#private_caches as well as https://stackoverflow.com/a/26813182

I created this branch months ago and promptly forgot about it entirely.
Now I anm cleaning old branches, here we are :)

[pep8speaks]

Hello @MonkeyDo! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2025-01-17 12:22:11 UTC

[mayhem]

Seems sensical, but I dont understand caching well enough. I think we should have @amCap1712 also look at this.

[MonkeyDo]

Quick ping to @amCap1712

[amCap1712]

I think we should add this for only responses that require authorization, like that determine the user based on the auth token in the request header but it's fine to do that later.