[identity] update transactwriteitems error log

Summary: current logs do not tell us exactly what ddb error we're seeing. we need to know what the error is to understand why it's occurring

Test Plan: locally confirmed that new log appears

Reviewers: will, bartek

Reviewed By: will

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13314

services/identity/src/database/one_time_keys.rs

@@ -141,6 +141,7 @@ impl DatabaseClient {
       match transaction {
         Ok(_) => return Ok((Some(otk_row.otk), requested_more_keys)),
         Err(e) => {
+          info!("Error retrieving one-time key: {:?}", e);
           let dynamo_db_error = DynamoDBError::from(e);
           let retryable_codes = HashSet::from([
             retry::CONDITIONAL_CHECK_FAILED,