Report Redis failed calls

[grcevski]

This PR does couple of things:

1. Tracks now failed Go Redis calls. We were previously ignoring them since there's no data, e.g. the server doesn't respond or even connect.
2. I noticed we didn't send db.system for OTel attributes, only Prometheus. I've added that now and I updated the tests to explicitly check.
3. I added error.type as attribute for metrics. According to the OTel spec, I can't see status code for DB metrics, but error type shouldn't be empty if there were errors. This way clients can determine if they have failing SQL or Redis calls.
4. I refactored the OATS tests to remove some duplication of files.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.71930% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.62%. Comparing base (8676f4e) to head (327565a).

Files	Patch %	Lines
pkg/internal/request/span_getters.go	72.22%	4 Missing and 1 partial ⚠️
pkg/internal/export/otel/metrics.go	50.00%	0 Missing and 1 partial ⚠️
pkg/internal/export/prom/prom.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #909      +/-   ##
==========================================
+ Coverage   78.53%   78.62%   +0.09%     
==========================================
  Files         132      132              
  Lines        9665     9688      +23     
==========================================
+ Hits         7590     7617      +27     
+ Misses       1565     1564       -1     
+ Partials      510      507       -3     

Flag	Coverage Δ
integration-test	54.71% <45.61%> (-0.18%)	⬇️
k8s-integration-test	56.06% <38.59%> (-0.12%)	⬇️
oats-test	36.40% <54.38%> (+0.19%)	⬆️
unittests	43.80% <54.38%> (-0.04%)	⬇️

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[mariomac]

LGTM!