chore: add show key command that prints the pub key (#49) #47

Job	Run time
go_sec_covenant_signer	1m 17s
lint_test / gosec	2m 29s
lint_test / check-mock-gen	0s
lint_test / build	28s
lint_test / integration-tests	7m 5s
lint_test / lint	35s
lint_test / unit-tests	1m 22s
docker_pipeline / dockerfile_lint	22s
docker_pipeline / prepare-metadata	1s
docker_pipeline / docker_build (linux/amd64, ubuntu-24.04)	3m 10s
docker_pipeline / docker_build (linux/arm64, ubuntu-24.04-arm64)	3m 30s
docker_pipeline / merge_ecr	15s
docker_pipeline / merge_dockerhub	14s
docker_pipeline / vulnerability_scan	31s
	21m 19s

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