otelconf: add tests for grpc exporters with different certificate configurations

[bacherfl]

This PR adds component tests for the otlp grpc exporters for logs/metrics/traces. The tests work by starting a simple grpc server that implements the Export interface of the respective signals, and records what is being sent to it. This should server as a way to verify that the otlp exporters created within this package are able to communicate with the server.

Closes #7222

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.1%. Comparing base (23d3857) to head (8d398c8).
Report is 19 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7233     +/-   ##
=======================================
+ Coverage   81.0%   81.1%   +0.1%     
=======================================
  Files        204     204             
  Lines      18080   18148     +68     
=======================================
+ Hits       14651   14729     +78     
+ Misses      3003    3000      -3     
+ Partials     426     419      -7     

see 10 files with indirect coverage changes

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[bacherfl]

@pellared this should be ready for review now - I'm not sure if a changelog entry is needed as this PR only adds tests.
The failing lint check seems to affect files that are not part of this PR, here I'm not sure how to address that

[pellared]

The failing lint check seems to affect files that are not part of this PR, here I'm not sure how to address that

From build failure

Working tree is not clean, did you forget to run "make precommit"?

Guessing that go mod tidy run is missing as modified: otelconf/go.mod 😉

[pellared]

I think this can help you: https://github.com/signalfx/splunk-otel-go/blob/0e047ccc5cc160f2ff4a96e45065e8a3178cccbc/distro/otel_test.go#L763-L849

[pellared]

Isn't this a workaround?
Shouldn't this work?

n, err := net.Listen("tcp", "127.0.0.1:0")
require.NoError(t, err)
tt.args.otlpConfig.Endpoint = ptr(n.Addr().String())

    --- FAIL: Test_otlpGRPCLogExporter/with_TLS_config_and_client_key (0.00s)
        /home/hello-there/repos/opentelemetry-go-contrib/otelconf/v0.3.0/log_test.go:814: 
            	Error Trace:	/home/hello-there/repos/opentelemetry-go-contrib/otelconf/v0.3.0/log_test.go:814
            	Error:      	Received unexpected error:
            	            	parse "127.0.0.1:44735": invalid URI for request
            	Test:       	Test_otlpGRPCLogExporter/with_TLS_config_and_client_key

Shouldn't we create a bug that the confiugration is not working e.g. for 127.0.0.1:4318?

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#configuration-options:

The option SHOULD accept any form allowed by the underlying gRPC client implementation.

CC @codeboten

[bacherfl]

yes, I added a comment for now indicating that this is a workaround - forgot to include that when I first stumbled over this