Add metricbeat receiver and E2E integration test

[leehinman]

Once elastic/beats#41738 is merged. We need to add metricbeat receiver to the available receivers

1. add metricbeat receiver to https://github.com/elastic/elastic-agent/blob/main/internal/pkg/otel/components.go
2. write an E2E integration test that proves it works, similar to

   elastic-agent/testing/integration/otel_test.go

   Line 828 in e983650

   func TestOtelFBReceiverE2E(t *testing.T) {

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)