Use platformdirs to find user configuration files #705

Job	Run time
Build dev-env (ubuntu-20.04)	1m 34s
build-container-image	8s
Build dev-env (ubuntu-22.04)	1m 28s
Build dev-env (ubuntu-24.04)	1m 20s
Build dev-env (ubuntu-24.10)	1m 23s
Build dev-env (debian-bullseye)	1m 32s
Build dev-env (debian-bookworm)	1m 22s
Build dev-env (debian-trixie)	1m 36s
Build dev-env (fedora-40)	1m 36s
Build dev-env (fedora-41)	1m 28s
	13m 27s

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