added array serialization to logging_exporter

[willarmiros]

Description: Bug fix - adds serialization of array attributes, including nested arrays, in the logging_exporter. This allows them to be printed like the primitive attribute types when debugging. AFAICT, there aren't any attributes with array values today, but they are permitted types in the spec, and I will be contributing a resource detector that uses array attributes in the future.

Testing: Added unit test

[codecov]

Codecov Report

Merging #1994 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1994      +/-   ##
==========================================
+ Coverage   91.49%   91.51%   +0.01%     
==========================================
  Files         282      282              
  Lines       16631    16641      +10     
==========================================
+ Hits        15217    15229      +12     
+ Misses        978      976       -2     
  Partials      436      436              

Impacted Files	Coverage Δ
exporter/loggingexporter/logging_exporter.go	89.96% <100.00%> (+1.03%)	⬆️

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[willarmiros]

The CI check that's failing does not appear related to this change:

# github.com/logzio/jaeger-logzio/store
/home/circleci/go/pkg/mod/github.com/logzio/jaeger-logzio@v0.0.0-20200826115713-de8961d427e3/store/store.go:41:14: cannot use store.writer (type *LogzioSpanWriter) as type spanstore.Writer in return argument:
	*LogzioSpanWriter does not implement spanstore.Writer (wrong type for WriteSpan method)
		have WriteSpan(*model.Span) error
		want WriteSpan(context.Context, *model.Span) error
/home/circleci/go/pkg/mod/github.com/logzio/jaeger-logzio@v0.0.0-20200826115713-de8961d427e3/store/store.go:46:14: cannot use store.reader (type *LogzioSpanReader) as type dependencystore.Reader in return argument:
	*LogzioSpanReader does not implement dependencystore.Reader (wrong type for GetDependencies method)
		have GetDependencies(time.Time, time.Duration) ([]model.DependencyLink, error)
		want GetDependencies(context.Context, time.Time, time.Duration) ([]model.DependencyLink, error)
FAIL	github.com/open-telemetry/opentelemetry-collector-contrib/exporter/logzioexporter [build failed]

[jrcamp]

Overall LGTM