Metric Monitoring Storage Layer

[shreyashankar]

Related to #241

We currently have 2 tables for outputs and feedback. We also need to create materialized views of the joined tables, one for each metric with its corresponding window size. We finally need to create metric value history tables for fast querying.

To Dos

• [x] Create Metric abstract class with compute function. Refactor Task class to include a registerMetric function.
• [x] In the registerMetric function, create materialized views on joins with relevant window sizes.
• [ ] Create metric val history table. Create triggers to run metric computations at the refresh rate / compute frequency.