[exporters/otlp/otlpmetric] Wrap upload metrics error to provide additional context

[lukestoward]

I've recently been investigating an unstructured error message that was being logged in a service that uses OTel tracing and metrics. The error message I was seeing looked like this:

context deadline exceeded: rpc error: code = DeadlineExceeded desc = context deadline exceeded

After spending significant time working through the code to identify where this was being logged, and what the root cause was, I've identified the issue. This PR is not related to the actual issue (this isn't an OTel issue), but it does make a small change to where the error is being handled to wrap the error to provide additional context information. This also aligns it with the error wrapping happening several lines below. With this change, the above message becomes:

failed to upload metrics: context deadline exceeded: rpc error: code = DeadlineExceeded desc = context deadline exceeded

Knowing that this error originated in the metrics exporter and specifically as part of the upload functionality would have saved me a lot of time. Hopefully, this small change will save others some time in the future.

[codecov]

Codecov Report

Merging #3974 (65ce305) into main (a261a0f) will increase coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3974   +/-   ##
=====================================
  Coverage   82.0%   82.0%           
=====================================
  Files        171     171           
  Lines      12969   12969           
=====================================
+ Hits       10643   10645    +2     
+ Misses      2106    2104    -2     
  Partials     220     220           

Impacted Files	Coverage Δ
exporters/otlp/otlpmetric/internal/exporter.go	67.2% <100.0%> (ø)

... and 2 files with indirect coverage changes