Make HTTP clients fit in the plugin hierarchy

[jbertran]

What does this PR do?

• Move HTTP and HTTP2 clients to ClientPlugin
• Stop subscribing to connect channels in all OutboundPlugins, since only cassandra actually uses this channel

Motivation

To introduce peer service (see #3177), it's helpful for all client/producer plugins to have at least OutboundPlugin in their inheritance path.

Plugin Checklist

• Unit tests.

Additional Notes

[github-actions]

Overall package size

Self size: 4.18 MB
Deduped: 58.38 MB
No deduping: 58.43 MB

Dependency sizes

name	version	self size	total size
@datadog/pprof	2.2.1	14.24 MB	15.12 MB
@datadog/native-iast-taint-tracking	1.4.1	14.85 MB	14.86 MB
@datadog/native-appsec	3.2.0	13.38 MB	13.39 MB
protobufjs	7.1.2	2.76 MB	6.55 MB
@datadog/native-iast-rewriter	2.0.1	2.09 MB	2.1 MB
@datadog/native-metrics	2.0.0	898.77 kB	1.3 MB
opentracing	0.14.7	194.81 kB	194.81 kB
semver	7.3.8	88.2 kB	118.6 kB
@datadog/sketches-js	2.1.0	109.9 kB	109.9 kB
lodash.sortby	4.7.0	75.76 kB	75.76 kB
lru-cache	7.14.0	74.95 kB	74.95 kB
ipaddr.js	2.0.1	59.52 kB	59.52 kB
ignore	5.2.0	48.87 kB	48.87 kB
import-in-the-middle	1.3.5	34.34 kB	38.81 kB
istanbul-lib-coverage	3.2.0	29.34 kB	29.34 kB
retry	0.10.1	27.44 kB	27.44 kB
lodash.uniq	4.5.0	25.01 kB	25.01 kB
limiter	1.1.5	23.17 kB	23.17 kB
lodash.kebabcase	4.1.1	17.75 kB	17.75 kB
lodash.pick	4.4.0	16.33 kB	16.33 kB
node-abort-controller	3.0.1	14.33 kB	14.33 kB
crypto-randomuuid	1.0.0	11.18 kB	11.18 kB
diagnostics_channel	1.1.0	7.07 kB	7.07 kB
path-to-regexp	0.1.7	6.78 kB	6.78 kB
koalas	1.0.2	6.47 kB	6.47 kB
methods	1.1.2	5.29 kB	5.29 kB
module-details-from-path	1.0.3	4.47 kB	4.47 kB

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[codecov]

Codecov Report

Merging #3178 (cfae42e) into master (d638b4b) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head cfae42e differs from pull request most recent head cac2cd6. Consider uploading reports for the commit cac2cd6 to get more accurate results

@@            Coverage Diff             @@
##           master    #3178      +/-   ##
==========================================
- Coverage   86.57%   86.56%   -0.01%     
==========================================
  Files         333      333              
  Lines       11934    11928       -6     
  Branches       33       33              
==========================================
- Hits        10332    10326       -6     
  Misses       1602     1602              

Impacted Files	Coverage Δ
packages/dd-trace/src/plugins/outbound.js	50.00% <ø> (ø)
...kages/datadog-plugin-cassandra-driver/src/index.js	93.33% <100.00%> (+1.66%)	⬆️
packages/datadog-plugin-http/src/client.js	96.90% <100.00%> (-0.10%)	⬇️
packages/datadog-plugin-http2/src/client.js	96.80% <100.00%> (-0.07%)	⬇️

... and 3 files with indirect coverage changes

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[pr-commenter]

Benchmarks

Comparing candidate commit cac2cd6 in PR branch jbertran/http-client-tree with baseline commit d638b4b in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 441 metrics, 31 unstable metrics.

[tlhunter]

This looks good to me. It makes sense that an HTTP client would extend from ClientPlugin, being a client and all.

This appears to be entirely a refactor, nothing new, and the untouched tests all pass.

That said I would like @rochdev to take a quick look.

[rochdev]

Why not keep it there? If there are no publishers, this doesn't impact anything.

[jbertran]

I wasn't sure of the impact of subscribing to a channel, so I removed it by default. I'll revert this so we have an easy way to grab connect events in every client.