[KeyManager] Refactor workload_service APIs to use protocol buffers (… #3309

Job	Run time
Lint ./ (ubuntu-latest, Go 1.24.x)	4m 5s
Lint ./launcher (ubuntu-latest, Go 1.24.x)	4m 57s
Generate/Build/Test (ubuntu-latest, x32, Go 1.24.x)	2m 50s
Lint ./keymanager (ubuntu-latest, Go 1.24.x)	3m 40s
Lint CGO (ubuntu-latest, Go 1.24.x)	3m 6s
Lint ./cmd (ubuntu-latest, Go 1.24.x)	3m 56s
Generate/Build/Test (ubuntu-latest, x64, Go 1.24.x)	6m 55s
Generate/Build/Test (macos-latest, arm64, Go 1.24.x)	1m 31s
Generate/Build/Test (macos-14-large, x64, Go 1.24.x)	1m 34s
	32m 34s

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