feat: add splunkhec receiver

[kalleep]

PR Description

This pr adds otelcol.receiver.splunkhec component. This is a wrapper for https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/splunkhecreceiver.

Currently this support all settings from upstream except ack. To support this we must also add support for AckExtention. We can wait with that until we see a need for it.

I did some manual testing that it works

otelcol.receiver.splunkhec "default" {
	output {
		logs = [otelcol.exporter.debug.default.input]
		metrics = [otelcol.exporter.debug.default.input]
	}	
}

otelcol.exporter.debug "default" {
	verbosity = "detailed"
}

Request to generate log:

curl http://localhost:8088/ -d '{"time": 1437522387, "source": "my_source", "sourcetype": "my_sample_data", "index": "my_index", "host": "my_host", "event": { "message": "some message", "severity": "Info" }}'

Request to generate metric:

curl http://localhost:8088/ -d '{"time": 1437522387, "source": "my_source", "sourcetype": "my_sample_data", "index": "my_index", "host": "my_host", "event": "metric", "fields": {"metric_name:single": 123 }]'

Which issue(s) this PR fixes

Fixes: #3080

Notes to the Reviewer

We had a lot of functions in different tests named getFreeAddr that did the same thing. I added this function to componenttests and reused it in every place I could find.

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[github-actions]

💻 Deploy preview available:

• https://deploy-preview-alloy-3440-zb444pucvq-vp.a.run.app/docs/alloy/latest/

[clayton-cornell]

There's a few other doc-related comments not yet applied. Do we need to discuss the suggestions? Or are they pending a commit?

[kalleep]

@clayton-cornell no they are fine, just missed them and have been busy getting fixing the ci