Add ingester server for metrics encoded protobuf

[cw9]

Add an ingester server that decodes metrics encoded in protobuf protocol.
This server is not enabled yet, it will be enabled once M3aggregater could send traffic in protobuf format

[codecov]

Codecov Report

Merging #1252 into master will increase coverage by <.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1252     +/-   ##
========================================
+ Coverage    70.6%   70.7%   +<.1%     
========================================
  Files         759     759             
  Lines       63828   63828             
========================================
+ Hits        45122   45131      +9     
+ Misses      15780   15773      -7     
+ Partials     2926    2924      -2

Flag	Coverage Δ
#aggregator	81.6% <ø> (ø)	⬆️
#cluster	85.7% <ø> (ø)	⬆️
#collector	78.4% <ø> (ø)	⬆️
#dbnode	80.7% <ø> (ø)	⬆️
#m3em	73.2% <ø> (ø)	⬆️
#m3ninx	75.4% <ø> (ø)	⬆️
#m3nsch	51.1% <ø> (ø)	⬆️
#metrics	18.2% <ø> (ø)	⬆️
#msg	75% <ø> (+0.1%)	⬆️
#query	60.5% <ø> (ø)	⬆️
#x	76% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7dd6c34...895ead9. Read the comment docs.

[jeromefroe]

LGTM