feat(spanner): add support for @ReadOnlyProperty#4336

bradperkins-gh wants to merge 3 commits intoGoogleCloudPlatform:mainGoogleCloudPlatform/spring-cloud-gcp:mainfrom

bradperkins-gh:support-read-only-property-spannerbradperkins-gh/spring-cloud-gcp:support-read-only-property-spannerCopy head branch name to clipboard