Nix build improvements (macOS support + image slimming) #2598

Job	Run time
Decide if Helm charts are pushed to the helm repository based on action trigger	4s
Run Cargo Deny (advisories)	25s
Run Cargo Deny (bans licenses sources)	22s
Run Rustfmt	15s
Run RustDoc	1m 9s
Run Cargo Udeps	1m 51s
Run Clippy	24s
Run Cargo Tests	36s
Check if committed README is the one we would render from the available parts	33s
Check if committed Helm charts are up to date	34s
All tests passed	3s
Package Charts, Build Docker Image and publish them - ubicloud-standard-8-arm	11m 11s
Package Charts, Build Docker Image and publish them - ubuntu-latest	12m 19s
Build and publish manifest list	39s
Run the OpenShift Preflight check on the published images	22s
	30m 47s

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