Preserve original error messages in OTLP exporter

[mwear]

Description:
I was troubleshooting an issue where un-retryable exports were being retried. #2455 fixes the root cause and this PR improves error messages from the OTLP exporter. The exporter returns the same permanent error instance for each export which masks the underlying error and makes failures hard to debug. This PR preserves the original error by wrapping it in a permament error and returning it.

Previously all log message looked as follows:

failed to push metrics data via OTLP exporter: Permanent error: fatal error sending to server

Now they preserve the original error message:

failed to push metrics data via OTLP exporter: Permanent error: rpc error: code = InvalidArgument desc = [otlp: empty data point]

[codecov]

Codecov Report

Merging #2459 (7618645) into main (9de6dd7) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main    #2459   +/-   ##
=======================================
  Coverage   91.76%   91.76%           
=======================================
  Files         265      265           
  Lines       15111    15111           
=======================================
  Hits        13867    13867           
  Misses        866      866           
  Partials      378      378           

Impacted Files	Coverage Δ
exporter/otlpexporter/otlp.go	71.79% <0.00%> (ø)

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