Specifiable indexes for topics

Currently all metrics from Mqtt or events from OPC go into the same metrics or event index.

For future ease of use and to conform with indexing best practices, it would be useful to be able to specify an index per topic. This would help with the following:

1. Data retention policy.

2. Data structuring (logical data separation and simpler SPL)

3. User rights (Restrict access)

4. Possible Compliance issues based on the above.