Extract service.pipelines interface

[djaglowski]

Subset of #6700

[codecov]

Codecov Report

Base: 90.67% // Head: 90.60% // Decreases project coverage by -0.07% ⚠️

Coverage data is based on head (707364e) compared to base (51c9139).
Patch coverage: 8.33% of modified lines in pull request are covered.

❗ Current head 707364e differs from pull request most recent head ad38f1f. Consider uploading reports for the commit ad38f1f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6764      +/-   ##
==========================================
- Coverage   90.67%   90.60%   -0.07%     
==========================================
  Files         241      242       +1     
  Lines       14525    14536      +11     
==========================================
  Hits        13171    13171              
- Misses       1087     1098      +11     
  Partials      267      267              

Impacted Files	Coverage Δ
service/graph.go	0.00% <0.00%> (ø)
service/host.go	89.47% <ø> (ø)
service/pipelines.go	93.93% <100.00%> (ø)

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[djaglowski]

cc @bogdandrutu

[djaglowski]

This PR establishes the "fork" between the current way of managing pipelines and the way of doing it via a graph that includes connectors. At the appropriate time, we can use a feature gate to toggle between the two implementations.

[bogdandrutu]

Need rebase.

[djaglowski]

I've rebased, but this basically required adding connector.Builder, which I've now spun off into #6867. Also added tests for other component builders in #6862.

[gbbr]

Hi Daniel & Bogdan! It would be very nice if we could add descriptions to these PRs

[djaglowski]

This is rebased onto #6867 and ready to go otherwise.

[TylerHelmuth]

LGTM

[jpkrohling]

Looks promising, but what's up with the tests? It would be nice to have a few tests demonstrating the graph. For instance, in the look from the last to first after sorting the graph, I assume the exporters are all located towards the end of the slice, with processors next, and receivers first. This is something that could be exemplified (and proven) in the tests.

[djaglowski]

Yeah, test coverage is poor on this PR. I think things are covered quite thoroughly on #6700, but some lower level tests would be better here. For now, what do you think about me removing the implementations of Start and Shutdown in this PR and then adding tests alongside the implementations later?

[djaglowski]

I've removed the implementations entirely, so now this is just adding the interface and a stub for the graph-based implementation. @open-telemetry/collector-approvers, please take a look.

[djaglowski]

@open-telemetry/collector-maintainers, I believe this is ready to merge.