Add required jaeger env var

[julianocosta89]

Changes

PR #1683 broke Jaeger as https://github.com/jaegertracing/jaeger/releases/tag/v1.59.0 had a breaking change.

This PR adds the missing env var to Jaeger.

@puckpuck we need this env var before getting #1687 merged and released.

Merge Requirements

For new features contributions please make sure you have completed the following
essential items:

• [ ] CHANGELOG.md updated to document new feature additions
• [ ] Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[puckpuck]

Hey @julianocosta89 I'm looking over how to implement this in Helm, and looking at the Helm charts themselves, it seems Jaeger wants this implemented by setting COLLECTOR_OTLP_ENABLED to true, and not the environment variable this PR is doing.

[puckpuck]

Here is the relevant code block for the Helm chart. The variable COLLECTOR_OTLP_GRPC_HOST_PORT is only set if the default port of 4317 is not used.

https://github.com/jaegertracing/helm-charts/blob/main/charts/jaeger/templates/collector-deploy.yaml#L65-L76

[julianocosta89]

@puckpuck have you seen the release notes from Jaeger?
https://github.com/jaegertracing/jaeger/releases/tag/v1.59.0

⛔ Breaking Changes
The OTEL Collector upgrade brought in a change where OTLP receivers started listening on localhost instead of 0.0.0.0 as before. As a result, when running in container environment the endpoints are likely unreachable from other containers (Issue jaegertracing/jaeger#5737). The fix will be available in the next release. Meanwhile, the workaround is to instruct Jaeger to listen on 0.0.0.0, as in this fix:
- COLLECTOR_OTLP_GRPC_HOST_PORT=0.0.0.0:4317
- COLLECTOR_OTLP_HTTP_HOST_PORT=0.0.0.0:4318

[julianocosta89]

If the behaviour is the same, I believe we must use the K8S downward API to get the pod_ip:4317.