feat(exporter-collector): log upstream error #1459

[vmarchaud]

As stated in the issue, before it was impossible to know why we couldnt push to the collector.

[obecny]

code wise it looks finne, can you fix build as it is failing everywhere ?

[codecov]

Codecov Report

Merging #1607 (2a6cdb5) into master (e78f65e) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1607      +/-   ##
==========================================
- Coverage   91.35%   91.32%   -0.04%     
==========================================
  Files         165      160       -5     
  Lines        5042     4771     -271     
  Branches     1040      978      -62     
==========================================
- Hits         4606     4357     -249     
+ Misses        436      414      -22     

Impacted Files	Coverage Δ
...kages/opentelemetry-exporter-collector/src/util.ts
.../opentelemetry-exporter-collector/src/transform.ts
...lemetry-exporter-collector/src/transformMetrics.ts
...ry-exporter-collector/src/CollectorExporterBase.ts

[vmarchaud]

@obecny I've rebased and fixed the build ! PTAL

[vmarchaud]

cc @open-telemetry/javascript-approvers this one only need one more review :)