Fix trace jaeger conversion to internal traces zero time bug

[pkositsyn]

Description:
Fixing a bug. When spans are converted from internal trace to jaeger trace the conversion is zero timestamp -> time.Time{} which is a reserved date. When converted back, this date is interpreted as a usual one, so ProtoBatchesToInternalTraces(InternalTracesToJaegerProto(traces)) != traces. So I added a check on this one

[codecov]

Codecov Report

Merging #1957 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1957   +/-   ##
=======================================
  Coverage   91.41%   91.41%           
=======================================
  Files         284      284           
  Lines       16788    16791    +3     
=======================================
+ Hits        15347    15350    +3     
  Misses       1009     1009           
  Partials      432      432           

Impacted Files	Coverage Δ
consumer/pdata/timestamp.go	100.00% <100.00%> (ø)
translator/trace/jaeger/jaegerproto_to_traces.go	91.00% <100.00%> (ø)
translator/internaldata/resource_to_oc.go	91.78% <0.00%> (ø)

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[tigrannajaryan]

Please add a test to verify the bug fix.

[pkositsyn]

Well, I think it is better to add function to timestamp package for that and test it there

[pkositsyn]

@tigrannajaryan does it look good now?

[tigrannajaryan]

LGTM. Thanks.