Prometheus style histogram metrics from statsd input plugin

## Feature Request
A way to generate Prometheus style histogram metrics from statsd input plugin (something similar to https://github.com/atlassian/gostatsd#timer-histograms-experimental-feature)

### Proposal:
Statsd Input plugin receives raw data from clients thus it should be possible to maintain counters for a user-defined set of le-buckets(similar to Prometheus). Le labels can be added as tags.

### Current behavior:
It is not possible to generate Prometheus style histogram metrics for statsd Input plugin.

### Desired behavior:
Generate Prometheus style histogram metrics for statsd Input plugin

### Use case:
This will add flexibility for conversion from statsd to Prometheus type data.

The issue does not name files or tests; begin by locating the statsd input plugin and the existing Prometheus metric conventions in the repository. Define how user-supplied le-buckets and tags should become histogram metrics, then add coverage showing the desired conversion from statsd input to Prometheus-style output.

Written by the indexing model from the issue text.