Use latest flat-manager-client

[ryonakano]

Problem

We use flat-manager-client from flat-manager repository in these places:

flatpak-platform/Dockerfile

Lines 13 to 14 in 5c3c307

	ADD https://raw.githubusercontent.com/flatpak/flat-manager/master/flat-manager-client /usr/bin
	RUN chmod +x /usr/bin/flat-manager-client

flatpak-platform/.github/workflows/daily.yml

Lines 43 to 46 in 5c3c307

	curl https://raw.githubusercontent.com/flatpak/flat-manager/0.3.7/flat-manager-client > ./flat-manager-client
	sudo mv ./flat-manager-client /usr/bin/flat-manager-client
	sudo chown root: /usr/bin/flat-manager-client
	sudo chmod +x /usr/bin/flat-manager-client

flatpak-platform/.github/workflows/release.yml

Lines 46 to 49 in 5c3c307

	curl https://raw.githubusercontent.com/flatpak/flat-manager/0.3.7/flat-manager-client > ./flat-manager-client
	sudo mv ./flat-manager-client /usr/bin/flat-manager-client
	sudo chown root: /usr/bin/flat-manager-client
	sudo chmod +x /usr/bin/flat-manager-client

We have two problems here:

• flat-manager-client is now ported from Python to Rust since 0.5.0-rc.2, resulting the first commands in Dockerfile no longer works
• The second and third occurrences use ancient version of flat-manager-client

Proposal

Use latest flat-manager-client that was ported to Rust. Probably we should fix to the latest tag, 0.5.1.

Prior Art (Optional)

No response