Nix build improvements (macOS support + image slimming) #16

Job	Run time
Check if committed Helm charts are up to date	2m 0s
Run Cargo Udeps	4m 37s
Run Cargo Deny (bans licenses sources)	31s
Run Cargo Tests	37s
Run Cargo Deny (advisories)	31s
Decide if Helm charts are pushed to the helm repository based on action trigger	5s
Run Clippy	31s
Run Rustfmt	16s
Run RustDoc	1m 54s
Check if committed README is the one we would render from the available parts	29s
All tests passed	3s
Package Charts, Build Docker Image and publish them - ubicloud-standard-8-arm	15s
Package Charts, Build Docker Image and publish them - ubuntu-latest	43s
Build and publish manifest list	-1s
Run the OpenShift Preflight check on the published images	-1s
	12m 30s

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