Add impi to ensure import organization

[ferhatelmas]

Similar to open-telemetry/opentelemetry-collector-contrib#42

Add impi to ensure import organization (std, 3rd party and local).

[codecov-io]

Codecov Report

Merging #426 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #426      +/-   ##
==========================================
+ Coverage   75.08%   75.11%   +0.02%     
==========================================
  Files         118      118              
  Lines        7234     7234              
==========================================
+ Hits         5432     5434       +2     
+ Misses       1538     1536       -2     
  Partials      264      264

Impacted Files	Coverage Δ
...iver/prometheusreceiver/internal/metricsbuilder.go	96.71% <ø> (ø)	⬆️
receiver/opencensusreceiver/factory.go	89.18% <ø> (ø)	⬆️
receiver/prometheusreceiver/metrics_receiver.go	74.46% <ø> (ø)	⬆️
...eceiver/prometheusreceiver/internal/transaction.go	75.75% <ø> (ø)	⬆️
observability/observability.go	50% <ø> (ø)	⬆️
...eceiver/opencensusreceiver/ocmetrics/opencensus.go	78.57% <0%> (+3.57%)	⬆️

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[tigrannajaryan]

Thank you.