flatpak-builder: Add ability to override artifact name #782

Job	Run time
Flatpak Builder (x86_64, use-cache, cache-restored)	1m 32s
Flatpak Builder with Dedicated Path Params	1m 32s
Tests (24.x)	23s
Flatpak Builder Stop At	1m 29s
Lint	24s
Flatpak Builder (x86_64, no-cache, no-cache-restored)	1m 29s
Flatpak Builder (x86_64, use-cache, no-cache-restored)	1m 34s
Tests (25.x)	23s
Flatpak Builder (aarch64, use-cache, cache-restored)	3m 15s
Flatpak Builder Debug Bundle	1m 31s
Flatpak Builder Cache Hit	1m 30s
	15m 2s

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