Use `confighttp` for target allocator http client

[swiatekm]

Component(s)

receiver/prometheus

Is your feature request related to a problem? Please describe.

We'd like to use TLS client authentication for communication between the collector and target allocator. A detailed discussion about the reasons can be found here: open-telemetry/opentelemetry-operator#1669.

Describe the solution you'd like

We should use go.opentelemetry.io/collector/config/confighttp. This is a standard for collector components and users should be comfortable with it. It will also give us a lot more customization for very little additional maintenance burden.

Describe alternatives you've considered

We could implement just the TLS options ourselves, but there doesn't seem to be any upside to that.

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/prometheus: @Aneurysm9 @dashpole

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[swiatekm]

If this sounds reasonable, you can assign this issue to me. I basically already have this change implemented, it's very small.

[dashpole]

This seems reasonable to me. Is it breaking, or additive?

[swiatekm]

Additive, the only common field is Endpoint, and the yaml key is the same. So it should be transparent to the user.

[dashpole]

Sounds great. Feel free to open the PR.

[atoulme]

#31452 is merged, can we close this issue?