Set BUILDBUDDY_RUN_ID env var (#11584)

I think this should be set in the env so that non-bazel tools can pick
it up and send it back via PARENT_RUN_ID metadata to show up as linked
workflow child invocations. LMK if there's a better way / something I'm
missing here?

Author: tylerwilliams

enterprise/server/cmd/ci_runner/main.go

@@ -725,6 +725,7 @@ func run() error {
 	}
 	ws.rootDir = rootDir
 	os.Setenv("BUILDBUDDY_CI_RUNNER_ROOT_DIR", rootDir)
+	os.Setenv(ci_runner_env.BuildBuddyRunIDEnvVarName, runID)
 
 	// Bazel needs a HOME dir; ensure that one is set.
 	if err := ensureHomeDir(); err != nil {

enterprise/server/util/ci_runner_env/ci_runner_env.go

@@ -3,6 +3,7 @@ package ci_runner_env
 const (
 	BuildBuddyAPIKeyEnvVarName       = "BUILDBUDDY_API_KEY"
 	BuildBuddyInvocationIDEnvVarName = "BUILDBUDDY_INVOCATION_ID"
+	BuildBuddyRunIDEnvVarName        = "BUILDBUDDY_RUN_ID"
 
 	BBGrpcClientOriginEnvVarName   = "BB_GRPC_CLIENT_ORIGIN"
 	BBGrpcClientIdentityEnvVarName = "BB_GRPC_CLIENT_IDENTITY"