fix: ensure environment variable precedence between env and envFrom

[MayorFaj]

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Changes

• Reversed the processing order in pkg/specgen/generate/kube/kube.go to process envFrom before env
• Added integration test to verify correct precedence behavior

Does this PR introduce a user-facing change?

Fix `kube play` to follow Kubernetes precedence order where `env` values override `envFrom` values for the same environment variable

Fixes #27287

[packit-as-a-service]

[NON-BLOCKING] Packit jobs failed. @containers/packit-build please check. Everyone else, feel free to ignore.

[TomSweeneyRedHat]

LGTM