Add metric filter option to metrics transform processor

[james-bebbington]

Link to tracking Issue: #1088 (comment)

Description:

Add a simple include filter option with strict or regexp match type so that transforms can be applied to a range of metrics. When using the regexp match type, new_name supports expansion.

This implementation is compatible with the config proposed here so could be switched out for that implementation in the future if desired. Also retained the metric_name config option for backwards compatibility but removed references to this from the documentation.

Continues optimizing for the strict match case, i.e. retain O(n) + O(t) for strict matches where metric names are unique, at the cost of making regexp matching slightly slower. regexp matches will be O(n) * O(t).

Also resolves an edge case where if multiple metrics have the same name only one of them would previously have been transformed.

Documentation:

Updated the documentation to specify how to use the match_type filter, and generally cleaned up the README to be more easily digested.

[codecov]

Codecov Report

Merging #1447 into master will increase coverage by 17.92%.
The diff coverage is 98.50%.

@@             Coverage Diff             @@
##           master    #1447       +/-   ##
===========================================
+ Coverage   70.87%   88.80%   +17.92%     
===========================================
  Files          29      341      +312     
  Lines        1298    16690    +15392     
===========================================
+ Hits          920    14822    +13902     
- Misses        321     1403     +1082     
- Partials       57      465      +408     

Flag	Coverage Δ
integration	70.80% <ø> (-0.08%)	⬇️
unit	88.08% <98.50%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
processor/metricstransformprocessor/factory.go	98.76% <96.66%> (ø)
...stransformprocessor/metrics_transform_processor.go	100.00% <100.00%> (ø)
receiver/awsecscontainermetricsreceiver/factory.go	100.00% <0.00%> (ø)
exporter/sentryexporter/utils.go	100.00% <0.00%> (ø)
receiver/k8sclusterreceiver/collection/cronjobs.go	100.00% <0.00%> (ø)
processor/groupbytraceprocessor/event.go	96.61% <0.00%> (ø)
...ceiver/k8sclusterreceiver/collection/daemonsets.go	94.28% <0.00%> (ø)
...ver/kubeletstatsreceiver/kubelet/stats_provider.go	55.55% <0.00%> (ø)
...r/alibabacloudlogserviceexporter/trace_exporter.go	75.00% <0.00%> (ø)
...ter/signalfxexporter/dimensions/dimensionupdate.go	90.90% <0.00%> (ø)
... and 321 more

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[jpkrohling]

Any reasoning for this value?

[james-bebbington]

Just seemed like a sensible default. If a user is using regexp match type, they probably expect more than 1 match.

[jpkrohling]

Sounds good. Perhaps add this as a comment to the code? Otherwise, it's still going to be a magic number :)

[jpkrohling]

Shouldn't this be transform.NewName?

[james-bebbington]

The metric name has been transformed at this point so either would work.

I wanted to use metric.MetricDescriptor.Name here so this works even if transform.NewName supports expansion (and thus the new name can differ from the raw value of transform.NewName).

I've now added expansion to this PR - see comment below.

[james-bebbington]

@jpkrohling FYI while addressing your comments, I also added one minor feature to this PR, which is that if the match_type is regexp, then new_name now supports regexp expansion, see the updated test case.