Support auth for otelcol.receiver components

[tpaschalis]

Request

The receiver components in the OpenTelemetry collector support authentication for incoming requests using the configauth package, in a similar-but-not-exact way to the how exporters use.

I don't remember this coming up in the past (thanks @srinivasmummareddy for opening a discussion around this in grafana/agent#6472) and couldn't find a similar issue so I opened this one.

Use case

Authenticating incoming requests to receiver components. We've held back from introducing this on the agent's root HTTP server, but maybe it makes sense to consider on a subset of components as a start.

[github-actions]

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[m4r1u2]

We also need this feature!

[mortaelth]

also hit the unsupported auth feature. It would be very useful. The upstream OpenTelemetry otelcol receiver supports it.