Setup synthetic metrics and test alerts on COS

[sudeephb]

• Setup a SyntheticCollector that exposes mock metrics on the hardware-observer unit on the default exporter port.
• Verify the alert rules are fired based on those metrics.
• The mock data of metrics and corresponding alerts are in the same place in mock_data.py, so it can be easily updated to include more data after this is accepted.

[sudeephb]

I also wanted to know whether we would be adding more data into mock_data.py down the line?

Yes, after this approach is accepted, we will add additional metrics(and corresponding alerts) in mock_data.py , and we can keep adding it in the future if we think we need more cases.