Enhance indexing custom metric

This is a change in an effort to enhance indexing correctness and latency via modifying the custom metric table we capture for indexing latencies.

• We want to identify, for every indexing message being processed, whether the action is for regular indexing (i.e. a record changed event) or re-indexing. This is captured via 'topicName' as a string value
• We want to capture if indexing succeeded (i.e. no DLQ activity). This is captured via 'success' as a boolean value