Added audit activities when secret variables are upserted

Added audit activities when secret variables are created or updated
through the `PUT /api/latest/fleet/spec/secret_variables` endpoint.

cmd/fleetctl/fleetctl/gitops_test.go

@@ -7441,7 +7441,9 @@ software:
 		t.Setenv("FLEET_SECRET_FOO", "someValue")
 		// The base mock provides ValidateEmbeddedSecretsFunc (used by scripts/batch),
 		// so leave it alone; only the secret-upload func needs a stub here.
-		ds.UpsertSecretVariablesFunc = func(ctx context.Context, secretVariables []fleet.SecretVariable) error { return nil }
+		ds.UpsertSecretVariablesFunc = func(ctx context.Context, secretVariables []fleet.SecretVariable) (created []string, updated []string, err error) {
+			return nil, nil, nil
+		}
 		ds.UpsertSecretVariablesFuncInvoked = false
 
 		yml := writeYAML(t, teamYAML(`  name_template: "iPad $FLEET_SECRET_FOO"`))