Adding mechanism to add field to all measurement (along with currently supported tags)

[atulaggarwal]

Currently we can add tags to all measurements. However tags are memory intensive and causes high cardinality in influxdb for tags with variable values. We need mechanism to add field to all measurements also.

Use case:
We run dropwizard application in k8s and we push name of the pod as tag to distinguish between various pod while looking at metrics. Due to large variation of pod name, the cardianlity of the influx has increased drastically and it is growing everyday (even after deleting old data).
We don't need it as tag as we only need to filter it while viewing and hence for this use case field makes more sense.