Disable System.Runtime EventCounters by default.

[cijothomas]

Starting with 2.8.0 of Asp.Net Core sdk, we were collecting a set of System.Runtime eventcounters by default.

Proposing to disable any counters collection by default:

1. These counters are sent as custom metric , and hence they are billed to the customers.
2. Since these are not free, its best to leave it upto the customer to add any eventcounter they are interested in.

(A set of PerformanceCounters are still collected by default - ApplicationInsights treats them as StandardMetrics and are hence not billed. Until Application Insights recognizes a set of EventCounters as StandardMetrics, we should stop collecting them by defualt)