Add sample rate support for counter, transfer gauge to double and tra…

[gavindoudou]

…nsfer counter to int only.

Description:

• Add sample rate support for counter
  If we receive counterName:10|c|@0.1, we will transfer the value to 10/0.1 = 100 to the following process
• Transfer gauge to double only
  After discussion, we plan to transfer gauge to double only no matter what we receive
  gaugeName:86|g will be transferred to 86.0 as Double_Gauge only
• Transfer counter to int only
  After discussion, we plan to transfer counter to int only no matter what we receive
  counterName:86|c will be transferred to 86 as Int only

Link to tracking Issue:

• Add StatsD receiver #290

Testing:

• Added unit tests

[bogdandrutu]

Not an expert in statsd protocol, @pmcollins @jrcamp take a look?

[keitwb]

This needs to be converted to use pdata.Metrics at some point, but for what your stated changes are this looks good.