[8.x](backport #6315) [otel] add loadbalancing exporter component

[mergify]

What does this PR do?

Adds the Otel loadbalancing exporter to the elastic-agent.

Why is it important?

It gives the ability to route logs, metrics or traces to different OTLP endpoints depending on the configured routing_key . This feature can be helpful when distributing the processing load among different collectors. For example, current APM OTLP data is directly processed with the lsminterval, elastictrace and signaltometrics components, but all those components could be moved from the collection/edge collectors to a set of collector that only handle data transformations. One of the main benefits of the latest approach is the separation of concerns, processing collectors would be part of another resource entity that would be managed independetly.

Sample configuration that routes traces based on their service.name key:

      exporters:
        loadbalancing/traces:
          routing_key: "service"
          protocol:
            otlp:
          resolver:
            # use k8s service resolver, if collector runs in kubernetes environment
            k8s:
              service: lb-svc.kube-public

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

---

This is an automatic backport of pull request #6315 done by [Mergify](https://mergify.com).

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube