Support XDG_BASE_DIRECTORY specification.

[mijoharas]

Please support the XDG_BASE_DIRECTORY specification instead of hardcoding config and app data into ~/.sentry.

other than admittedly being a bit of a pet peeve of lots of people due to making the home directory messy, it also fails means the cli fails to work if you are using a coding agent and have blocked writes to your home directory.

[BYK]

Emitting to home directory is actually our last resort. Most other locations are usually write-protected and require sudo which we don't want. Let me see what we can do here.