[chore] Support connector in metrics.go.tmpl NewMetricsBuilder

[Dainerx]

Description

I discovered this issue while trying to upgrade the opentelemetry collector from v0.111.0 to v0.119.0 that was released two weeks ago. To reproduce please take a look at the issue below.

Link to tracking issue

Fixes #12402

Testing

Run make generate on a processor or connector component

[codecov]

Codecov Report

Attention: Patch coverage is 82.60870% with 16 lines in your changes missing coverage. Please review.

Project coverage is 92.15%. Comparing base (56fbf4c) to head (247a505).

Files with missing lines	Patch %	Lines
cmd/mdatagen/internal/sampleconnector/factory.go	40.00%	6 Missing ⚠️
...pleconnector/internal/metadata/generated_config.go	83.78%	4 Missing and 2 partials ⚠️
...econnector/internal/metadata/generated_resource.go	91.11%	4 Missing ⚠️

❌ Your patch check has failed because the patch coverage (82.60%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12403      +/-   ##
==========================================
- Coverage   92.18%   92.15%   -0.04%     
==========================================
  Files         465      468       +3     
  Lines       25275    25367      +92     
==========================================
+ Hits        23301    23377      +76     
- Misses       1575     1589      +14     
- Partials      399      401       +2     

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[bogdandrutu]

@Dainerx what other component do you have that emits metrics?

[Dainerx]

@bogdandrutu in my use case, processors and connectors do emit metrics.

My main concern is the if statement surrounding only the function signature. Also, I expected adding a new class in the metadata schema.

[bogdandrutu]

My main concern is the if statement surrounding only the function signature. Also, I expected adding a new class in the metadata schema.

That should be fixed.

processors and connectors do emit metrics.

How come? I can see why connectors may do it, but how come the processors?

[Dainerx]

How come? I can see why connectors may do it, but how come the processors?

Processors can have mutate data capabilities, the metrics generation processor does generate metrics. Although, this is possible, I agree with you it's not a best practice to use a processor to generate metrics.

I am fine with only supporting connector scrapper, and receiver. We should also:

1. Add a sample connector to be used for testing purposes to check the output of mdatagen against it
2. Update the README file.

WDYT?

[bogdandrutu]

I am ok with this proposal.

[bogdandrutu]

I am not sure what changed, but this looks very strange that every line is updated.

[sincejune]

Suggested change

	* metrics emitted in the case of a scraping receiver, a scrapper, or a connector
	* metrics emitted in the case of a scraping receiver, a scraper, or a connector

[sincejune]

it should look like metrics_to_metrics for connectors

[sincejune]

Suggested change

	// NewFactory returns a receiver.Factory for sample receiver.
	// NewFactory returns a connector.Factory for sample connector.

[sincejune]

Suggested change

	# Sample metadata file with all available configurations for a receiver.
	# Sample metadata file with all available configurations for a connector.