Find better method to protect PrivateJsonFile on Windows

Find a better way to protect the PrivateJsonFile on Windows that doesn't rely on Unix file permissions, because that is just not working very well.

This is a follow up ticket for:

• Issue https://github.com/Open-EO/openeo-python-client/issues/387
• and PR: https://github.com/Open-EO/openeo-python-client/pull/399

Problem

We tried oschmod as a solution to restrict access to the PrivateJsonFile on Windows, because it seems to have a better implementation of Unix file permissions, though it still has limitations.

However, it is now clear that we have users for whom the oschmod solution did not work, so this route is a bit of a dead end.

Windows has an entirely different system for file permissions, and there can be a lot of other things that may prevent users from restricting access to files they have file ownership of. (Possibly there are security policies and such that prevent this)

To be decided

A) Either we just accept that on Windows the PrivateJsonFile will not be as strongly protected as on Linux and Mac OS and leave it at that.

Or B) we need to find an entirely different protection method on Windows that is better supported than Unix-style file permissions.

Start by reading issue 387 and PR 399, then review the current oschmod-based protection of PrivateJsonFile described there. Investigate Windows file-permission constraints and possible alternatives; done means reaching and documenting a decision between accepting weaker protection and adopting a better-supported Windows method.